Time filter

Source Type

Stockholm, Sweden

The Royal Institute of Technology is a university in Stockholm, Sweden. KTH was founded in 1827 as Sweden's first polytechnic and is one of Scandinavia's largest institutions of higher education in technology. KTH accounts for one-third of Sweden's technical research and engineering education capacity at university level. KTH offers programmes leading to a Master of Architecture, Master of Science in Engineering, Bachelor of Science in Engineering, Bachelor of Science, Master of Science, licentiate or doctoral degree. The university also offers a technical preparatory programme for non-scientists and further education.There are a total of just over 14 000 full-year equivalent undergraduate students, more than 1700 active postgraduate students and 4600 full-time-equivalent employees. KTH is one of the leading technical universities in Europe and highly respected worldwide, especially in the domains of technology and natural science. Wikipedia.

Gudnason S.B.,KTH Royal Institute of Technology | Nitta M.,Keio University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

We construct a D-brane soliton, a composite topological soliton sharing some properties with a D-brane, in a Skyrme model in 4+1 dimensions, in which Skyrmions are strings ending on a domain wall. We further generalize this D-brane soliton to diverse dimensions. A string, carrying the πN-1 topological charge, ends on a domain wall in an O(N) model with higher-derivative terms in N+1 dimensions. © 2015 American Physical Society. Source

Neretnieks I.,KTH Royal Institute of Technology
Applied Geochemistry | Year: 2014

In nuclear waste repositories concrete and bentonite are used, sometimes in contact with each other. The rate of mutual degradation of concrete and bentonite by alkaline fluids from concrete is explored using a simple model. The model considers dissolution of a soluble compound in the concrete (e.g. portlandite), which is gradually dissolved as the solubilised hydroxide and the cation(s) diffuse towards and into the bentonite in which smectite degrades by interaction with the solutes. Accounting for only the diffusion resistances in concrete and clay, the solubility of the concrete compound and the hydroxide consumption capacity of the smectite, results in a very simple analytical model. The model is tested against several published modelling results that account for reaction kinetics, reactive surface, and equilibrium data for tens to many tens of different secondary minerals. In the models that include several specified minerals often assumptions need to be made on which minerals can form. This introduces subjective assumptions. The degradation rates using the simple model are within the range of results obtained by the complex models. In the studies of the data used in these models it was found that the uncertainties in thermodynamic data are considerable and can give contradictory information on under what conditions smectite degrades. Some smectite models and thermodynamic data suggest that smectite will transform to other minerals spontaneously if there were no kinetic restrictions. © 2014 Elsevier Ltd. Source

Wang M.,Dalian University of Technology | Sun L.,Dalian University of Technology | Sun L.,KTH Royal Institute of Technology
ChemSusChem | Year: 2010

Photocatalytic hydrogen production by noble-metal-free molecular catalysts and related nanomaterials is discussed in this Highlight. Several recent nanomaterials, incorporating Fe- and Ni-based molecular catalysts, are highly effective for photo- and electrochemical hydrogen production, with good stabilities. © 2010 Wiley-VCH Verlag GmbH& Co. KGaA, Weinheim. Source

Wubben D.,ITG | Seethaler D.,Vienna University of Technology | Jalden J.,KTH Royal Institute of Technology | Matz G.,European Union
IEEE Signal Processing Magazine | Year: 2011

Lattice reduction is a powerful concept for solving diverse problems involving point lattices. Signal processing applications where lattice reduction has been successfully used include global positioning system (GPS), frequency estimation, color space estimation in JPEG pictures, and particularly data detection and precoding in wireless communication systems. In this article, we first provide some background on point lattices and then give a tutorial-style introduction to the theoretical and practical aspects of lattice reduction. We describe the most important lattice reduction algorithms and comment on their performance and computational complexity. © 2006 IEEE. Source

Zaman A.U.,KTH Royal Institute of Technology
International Journal of Environmental Science and Technology | Year: 2010

The aim of the study is to analyze three different waste treatment technologies by life cycle assessment tool. Sanitary Landfill, Incineration and gasification-pyrolysis of the waste treatment technologies are studied in SimaPro software based on input-output materials flow. SimaPro software has been applied for analyzing environmental burden by different impact categories. All technologies are favorable to abiotic and ozone layer depletion due to energy recovery from the waste treatment facilities. Sanitary landfill has the significantly lower environmental impact among other thermal treatment while gases are used for fuel with control emission environment. However, sanitary landfill has significant impact on photochemical oxidation, global warming and acidification. Among thermal technology, pyrolysis-gasification is comparatively more favorable to environment than incineration in global warming, acidification, eutrophication and eco-toxicity categories. Landfill with energy recovery facilities is environmentally favorable. However, due to large land requirement, difficult emission control system and long time span, restriction on land filling is applying more in the developed countries. Pyrolysis-gasification is more environmental friendly technology than incineration due to higher energy recovery efficiency. Life cycle assessment is an effective tool to analyze waste treatment technology based on environmental performances. © IRSEN, CEERS, IAU. Source

Moberg C.,KTH Royal Institute of Technology
Topics in Organometallic Chemistry | Year: 2012

Asymmetric allylic substitutions catalyzed by molybdenum and tungsten complexes provide branched chiral products from unsymmetrically substituted allylic reagents. Highly selective chiral ligands are available for both types of reactions, but for the tungsten-catalyzed substitutions, enantioselective reactions are only possible starting from achiral linear allylic substrates. A variety of stabilized carbanions can be used as nucleophiles. The molybdenum-catalyzed reaction has been applied to the synthesis of several biologically active compounds. © 2011 Springer-Verlag Berlin Heidelberg. Source

The biomechanical behaviour of biological cells is of great importance in many physiological processes. One such process is the maintenance of fibrous networks, such as collagenous tissues. The activity of the fibre-producing cells in this type of tissue is very important, and a comprehensive material description needs to incorporate the activity of the cells. In biomechanics, continuum mechanics is often employed to describe deforming solids, and modelling can be much simplified if continuum mechanics entities, such as stress and strain, can be correlated with cell activity. To investigate this, a continuum mechanics framework is employed in which remodelling of a collagen gel is modelled. The remodelling is accomplished by fibroblasts, and the activity of the fibroblasts is linked to the continuum mechanics theory. The constitutive model for the collagen fabric is formulated in terms of a strain energy function, which includes a density function describing the distribution of the collagen fibre orientation. This density function evolves according to an evolution law, where fibroblasts reorient fibres towards the direction of increasing Cauchy stress, elastic deformation, or stiffness. The theoretical framework is applied to experimental results from collagen gels, where gels have undergone remodelling under both biaxial and uniaxial constraint. The analyses indicated that criteria 1 and 2 (Cauchy stress and elastic deformations) are able to predict the collagen fibre distribution after remodelling, whereas criterion 3 (current stiffness) is not. This conclusion is, however, tentative and pertains, strictly speaking, only to fibre remodelling processes, and may not be valid for other types of cell activities. © 2009 Elsevier Ltd. All rights reserved. Source

Stilbs P.,KTH Royal Institute of Technology
Journal of Magnetic Resonance | Year: 2010

It is demonstrated that very robust spectral component separation can be achieved through global least-squares CORE data analysis of automatically or manually selected spectral regions in complex NMR spectra in a high-resolution situation. This procedure (acronym RECORD) only takes a few seconds and quite significantly improves the effective signal/noise of the experiment as compared to individual frequency channel fitting, like in the generic HR-DOSY approach or when using basic peak height or integral fitting. Results from RECORD processing can be further used as starting value estimates for subsequent CORE analysis of spectral data with higher degree of spectral overlap. © 2010 Elsevier Inc. All rights reserved. Source

Jonsson M.,KTH Royal Institute of Technology
Israel Journal of Chemistry | Year: 2014

Interfacial radiation chemistry is of key importance in nuclear technology because most materials in the vicinity of radioactive materials in nuclear power plants, reprocessing plants, and repositories for nuclear waste are exposed to ionizing radiation. Corrosion is a crucial issue for the long-term performance and safety of these installations. Nevertheless, this field is still fairly undeveloped. In this paper, the current state of the art with particular focus on reactions between aqueous radiolysis products and metal or metal oxide surfaces is discussed. The general reactivity of hydrogen peroxide and the hydroxyl radical towards oxide surfaces is discussed on the basis of recent experimental results and DFT calculations. More specific discussions on radiation-induced surface processes in a future geological repository for spent nuclear fuel are given as relevant examples. This includes radiation-induced dissolution of spent nuclear fuel in contact with groundwater, radiation-induced corrosion of copper, and radiation-induced alterations of bentonite clay. Current knowledge gaps in these areas are highlighted. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Edstrom A.,KTH Royal Institute of Technology
Physica C: Superconductivity and its Applications | Year: 2013

A systematic numerical study of non-pairwise vortex interaction forces in the Ginzburg-Landau model for single-and multicomponent superconductivity is presented. The interactions are obtained by highly accurate numerical free energy minimization. In particular a three-body interaction is defined as the difference between the total interaction and sum of pairwise interactions in a system of three vortices and such interactions are studied for single and two-component type-1, type-2, and type-1.5 superconductors. In the investigated regimes, the three-body interaction is found to be short-range repulsive but long-range attractive in the type-1 case, zero in the critical κ (Bogomoln'y) case, attractive in the type-2 case and repulsive in the type-1.5 case. Some systems of four vortices are also studied and results indicate that four-body forces are of substantially less significance than the three-body interactions. © 2013 Elsevier B.V. All rights reserved. Source

Rapp O.,KTH Royal Institute of Technology
Physical Review B - Condensed Matter and Materials Physics | Year: 2016

The zero-temperature conductivity σ(0) of icosahedral (i)-AlPdRe has been found to be simply related to the resistance ratio R=ρ4.2K/ρ295K by a power law, σ(0)∼R-1.74, over four orders of magnitude in σ(0). This relation includes metallic single grain samples, and polygrain samples of different morphologies which are metallic for small R values, and insulatinglike at large R. Electronic transport properties of single grain i-AlPdRe samples are thus found to be on common ground with polygrain i-AlPdRe. The relation between R and σ(0) can be qualitatively understood from published band-structure calculations on quasicrystalline approximants. © 2016 American Physical Society. Source

Cvetkovic V.,KTH Royal Institute of Technology
Environmental Research Letters | Year: 2011

A generalized distribution for the water residence time in hydrological transport is proposed in the form of the tempered one-sided stable (TOSS) density. It is shown that limiting cases of the TOSS distribution recover virtually all distributions that have been considered in the literature for hydrological transport, from plug flow to flow reactor, the advection-dispersion model, and the gamma and Levy densities. The stable property of TOSS is particularly important, enabling a seamless transition between a time-domain random walk, and the Lagrangian (trajectory) approach along hydrological transport pathways. © 2011 IOP Publishing Ltd. Source

Silaev M.,KTH Royal Institute of Technology
Physical Review B - Condensed Matter and Materials Physics | Year: 2016

Magnetic properties of dirty multiband superconductors near the upper critical field are studied. The parameter κ2 characterizing magnetization slope is shown to have a significant temperature variation which is quite sensitive to the pairing interactions and relative strengths of intraband impurity scattering. In contrast to single-band superconductors the increase of κ2 at low temperatures can be arbitrarily large determined by the ratio of maximal and minimal diffusion coefficients in different bands. Temperature dependencies of κ2(T) in two-band MgB2 and iron-based superconductors are shown to be much more sensitive to the multiband effects than the upper critical field Hc2(T). © 2016 American Physical Society. Source

Hendriks R.C.,Technical University of Delft | Gerkmann T.,KTH Royal Institute of Technology
IEEE Transactions on Audio, Speech and Language Processing | Year: 2012

For multi-channel noise reduction algorithms like the minimum variance distortionless response (MVDR) beamformer, or the multi-channel Wiener filter, an estimate of the noise correlation matrix is needed. For its estimation, it is often proposed in the literature to use a voice activity detector (VAD). However, using a VAD the estimated matrix can only be updated in speech absence. As a result, during speech presence the noise correlation matrix estimate does not follow changing noise fields with an appropriate accuracy. This effect is further increased, as in nonstationary noise voice activity detection is a rather difficult task, and false-alarms are likely to occur. In this paper, we present and analyze an algorithm that estimates the noise correlation matrix without using a VAD. This algorithm is based on measuring the correlation of the noisy input and a noise reference which can be obtained, e.g., by steering a null towards the target source. When applied in combination with an MVDR beamformer, it is shown that the proposed noise correlation matrix estimate results in a more accurate beamformer response, a larger signal-to-noise ratio improvement and a larger instrumentally predicted speech intelligibility when compared to competing algorithms such as the generalized sidelobe canceler, a VAD-based MVDR beamformer, and an MVDR based on the noisy correlation matrix. © 2011 IEEE. Source

Toll S.,KTH Royal Institute of Technology
Acta Mechanica | Year: 2011

Standard hypoplasticity is examined with respect to the thermodynamic requirement of non-negative energy dissipation. We introduce a stress energy function and derive a dissipation inequality in terms of the stress-dependent operators of the hypoplastic law. A general form for the non-linear operator is also found, which makes it straightforward to construct thermodynamically consistent hypoplasticity laws. We further examine the subclass of hypoplasticity where the linear term is non-dissipative and construct some examples of hypoplastic laws based on a quadratic stress energy function. © 2011 The Author(s). Source

Shirabe T.,KTH Royal Institute of Technology
Computers, Environment and Urban Systems | Year: 2012

Map algebra is a methodology for organizing and processing digital cartographic data in a geographic information system (GIS). While its capabilities to describe patterns existing (or hidden) in data have been well studied, its capabilities to prescribe new patterns in response to specific requirements have not been much explored. The latter, prescriptive capabilities help planners address a class of spatial problems called " cartographic allocation" (. Tomlin, 1990), which concerns allocation of subsets (or zones) of a cartographic space to certain uses according to one or more criteria. Taking a school districting problem as an example, this paper introduces a systematic approach to designing a map algebraic procedure for a cartographic allocation problem with capacity constraints. It is found that a classical trial-and-error heuristic can be refined to a more formal approximation method and serve as a good alternative to other solution methods when the problem involves a large number of spatial units as is often the case with a raster-based GIS. © 2011 Elsevier Ltd. Source

Ostling M.,KTH Royal Institute of Technology
Science China Information Sciences | Year: 2011

Silicon carbide (SiC) semiconductor devices for high power applications are now commercially available as discrete devices. Recently Schottky diodes are offered by both USA and Europe based companies. Active switching devices such as bipolar junction transistors (BJTs), field effect transistors (JFETs and MOSFETs) are now reaching the market. The interest is rapidly growing for these devices in high power and high temperature applications. The main advantages of wide bandgap semiconductors are their very high critical electric field capability. From a power device perspective the high critical field strength can be used to design switching devices with much lower losses than conventional silicon based devices both for on-state losses and reduced switching losses. This paper will review the current state of the art in active switching device performance for both SiC and GaN devices. SiC material quality and epitaxy processes have greatly improved and degradation free 100 mm wafers are readily available. This is encouraging since also bipolar devices now are attractive with good long term stability. SiC wafers still have a too high cost to be fully cost efficient. However, the SiC wafer roadmap looks very favorable as volume production takes off. For GaN materials the main application area is geared towards the lower power rating level up to 1 kV on mostly lateral FET designs. The cost advantage is interesting for GaN when grown on Si substrates to bring down costs. © Science China Press and Springer-Verlag Berlin Heidelberg 2011. Source

Gudnason S.B.,KTH Royal Institute of Technology | Nitta M.,Keio University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

We study a Skyrme-type model with a potential term motivated by Bose-Einstein condensates (BECs), which we call the BEC Skyrme model. We consider two flavors of the model: the first is the Skyrme model, and the second has a sixth-order derivative term instead of the Skyrme term, both with the added BEC-motivated potential. The model contains toroidally shaped Skyrmions, and they are characterized by two integers P and Q, representing the winding numbers of two complex scalar fields along the toroidal and poloidal cycles of the torus, respectively. The baryon number is B=PQ. We find stable Skyrmion solutions for P=1,2,3,4,5 with Q=1, while for P=6 and Q=1, it is only metastable. We further find that configurations with higher Q>1 are all unstable and split into Q configurations with Q=1. Finally we discover a phase transition, possibly of first order, in the mass parameter of the potential under study. © 2015 American Physical Society. Source

Cvetkovic V.,KTH Royal Institute of Technology
Water Resources Research | Year: 2012

A power-law extension of the gamma distribution is proposed as a general memory function for capturing rate limitations of retention in groundwater transport. Using moments, we show how the new memory function can be reduced to most other forms available in the literature, exactly or approximately. The proposed formulation is suitable for field scale or laboratory scale transport modeling. Rate limitation effects are illustrated for solute transport by considering the fractional mass release over a given transport scale. The equilibrium and no-retention cases set bounds for contaminant attenuation, between which the impact of rate limitations is clearly exposed. Source

Littke H.,KTH Royal Institute of Technology
Urban Forestry and Urban Greening | Year: 2016

One day in 2005, a bench, some grass, and a tree suddenly appeared on a parking spot in central San Francisco. The parking meter was paid for two hours, and after that the installation disappeared. This action by the art-design-activist organization Rebar has led to the annual global event Park(ing) Day and an official planning program in San Francisco, From Pavements to Parks, inspiring cities around the world to introduce their own parklet projects.Many cities are facing challenges such as economic deficits and a lack of open public spaces, and growing concerns exist regarding the need for urban greenery. This paper discusses how parklets are challenging the role of public spaces and urban nature, drawing on discussions and conceptualizations of publicness, observational data, literature review, and document analysis to explore the influence of parklets as an urban design strategy at a local and global level.The symbolic change from parking space to public park space and the tactical urbanism inspiration of the concept constitute both parts of the symbolic value of parklets. At the same time, the line between community activism and urban strategy has been blurred. The city reviews, permits, and inspects the projects; and the sponsor is responsible for the design, financing, maintenance, and liability. The paper concludes that, even though parklets might provide a new public space and bring greenery to streetscapes, publicness, roles and responsibility, as well as the functionality of nature in these projects, remain crucial questions. © 2016 Elsevier GmbH. Source

Brandenburg A.,KTH Royal Institute of Technology | Brandenburg A.,University of Stockholm
Astrophysical Journal | Year: 2014

Using direct numerical simulations of three-dimensional hydromagnetic turbulence, either with helical or non-helical forcing, we show that the kinetic-to-magnetic energy dissipation ratio always increases with the magnetic Prandtl number, i.e., the ratio of kinematic viscosity to magnetic diffusivity. This dependence can always be approximated by a power law, but the exponent is not the same in all cases. For non-helical turbulence, the exponent is around 1/3, while for helical turbulence it is between 0.6 and 2/3. In the statistically steady state, the rate of energy conversion from kinetic into magnetic by the dynamo must be equal to the Joule dissipation rate. We emphasize that for both small-scale and large-scale dynamos, the efficiency of the energy conversion depends sensitively on the magnetic Prandtl number, and thus on the microphysical dissipation process. To understand this behavior, we also study shell models of turbulence and one-dimensional passive and active scalar models. We conclude that the magnetic Prandtl number dependence is qualitatively best reproduced in the one-dimensional model as a result of dissipation via localized Alfvén kinks. © 2014. The American Astronomical Society. All rights reserved. Source

Brandenburg A.,KTH Royal Institute of Technology | Brandenburg A.,Albanova University Center | Stepanov R.,RAS Institute of Continuous Media Mechanics
Astrophysical Journal | Year: 2014

Using one-dimensional models, we show that a helical magnetic field with an appropriate sign of helicity can compensate the Faraday depolarization resulting from the superposition of Faraday-rotated polarization planes from a spatially extended source. For radio emission from a helical magnetic field, the polarization as a function of the square of the wavelength becomes asymmetric with respect to zero. Mathematically speaking, the resulting emission occurs then either at observable or at unobservable (imaginary) wavelengths. We demonstrate that rotation measure (RM) synthesis allows for the reconstruction of the underlying Faraday dispersion function in the former case, but not in the latter. The presence of positive magnetic helicity can thus be detected by observing positive RM in highly polarized regions in the sky and negative RM in weakly polarized regions. Conversely, negative magnetic helicity can be detected by observing negative RM in highly polarized regions and positive RM in weakly polarized regions. The simultaneous presence of two magnetic constituents with opposite signs of helicity is shown to possess signatures that can be quantified through polarization peaks at specific wavelengths and the gradient of the phase of the Faraday dispersion function. Similar polarization peaks can tentatively also be identified for the bi-helical magnetic fields that are generated self-consistently by a dynamo from helically forced turbulence, even though the magnetic energy spectrum is then continuous. Finally, we discuss the possibility of detecting magnetic fields with helical and non-helical properties in external galaxies using the Square Kilometre Array. © 2014. The American Astronomical Society. All rights reserved. Source

Sou K.C.,KTH Royal Institute of Technology | Rantzer A.,Lund University
Automatica | Year: 2012

In this paper a controller reduction method for discrete-time linear time-invariant systems is described. Using the bounded-real lemma, the proposed method generates reduced controllers with closed loop stability and H∞ norm performance guarantee. Information of the full controller is used as a basis for reduction using singular value decomposition. This is different from traditional model reduction schemes such as weighted balanced truncation. Numerical assessment of the proposed method is given in the end of the paper. © 2012 Elsevier Ltd. All rights reserved. Source

Shames I.,KTH Royal Institute of Technology | Dasgupta S.,University of Iowa | Fidan B.,University of Waterloo | Anderson B.D.O.,Australian National University
IEEE Transactions on Automatic Control | Year: 2012

Consider an agent A at an unknown location, undergoing sufficiently slow drift, and a mobile agent B that must move to the vicinity of and then circumnavigate A at a prescribed distance from A. In doing so, B can only measure its distance from A, and knows its own position in some reference frame. This paper considers this problem, which has applications to surveillance and orbit maintenance. In many of these applications it is difficult for B to directly sense the location of A, e.g. when all that B can sense is the intensity of a signal emitted by A. This intensity does, however provide a measure of the distance. We propose a nonlinear periodic continuous time control law that achieves the objective using this distance measurement. Fundamentally, a) B must exploit its motion to estimate the location of A, and b) use its best instantaneous estimate of where A resides, to move itself to achieve the circumnavigation objective. For a) we use an open loop algorithm formulated by us in an earlier paper. The key challenge tackled in this paper is to design a control law that closes the loop by marrrying the two goals. As long as the initial estimate of the source location is not coincident with the intial position of B, the algorithm is guaranteed to be exponentially convergent when A is stationary. Under the same condition, we establish that when A drifts with a sufficiently small, unknown velocity, B globally achieves its circumnavigation objective, to within a margin proportional to the drift velocity. © 2011 IEEE. Source

Eller D.,KTH Royal Institute of Technology
Journal of Aircraft | Year: 2012

A variable-order finite-element method for the solution of the steady nonlinear potential flow equations is presented. To achieve robustness and computational efficiency, the formulation is restricted to purely subsonic flow by means of a density modification in sonic flow regions. A test case that triggers the activation of this modification is presented to show that the method yields pressure results that are very close to those obtained with a mature Euler solver while reducing computational cost by an order of magnitude. Linear and quadratic elements are implemented, and the substantial benefit of using higher-order elements is demonstrated by means of a mesh-convergence study, showing how the convergence of induced drag and neutral point location is improved by the use of quadratic elements. For large surface meshes, the computational cost is found to be competitive with a linearized-potential boundary-element code accelerated by panel clustering. Copyright © 2011 by the American Institute of Aeronautics and Astronautics, Inc. Source

Cheng M.,Dalian University of Technology | Yang X.,Dalian University of Technology | Li S.,Dalian University of Technology | Wang X.,Dalian University of Technology | And 2 more authors.
Energy and Environmental Science | Year: 2012

A new iodine-free electrolyte based on amino acids L-cysteine/L-cystine as a redox couple has been designed and synthesized. DSSCs fabricated with the conventional I -/I 3 - redox couple gave efficiencies of 8.1% and 6.3% under optimized experimental conditions based on ruthenium dye, N719, and metal-free organic dye, TH202, respectively. Based on the same dyes, the DSSCs employing the new L-cysteine/L-cystine redox couple showed comparable efficiencies of 7.7% and 5.6%, respectively. However, higher incident-photon-to-electron (IPCE) conversion efficiencies and larger J sc values were found for devices with the L-cysteine/L-cystine redox couple than with I -/I 3 -. From an electrochemical impedance spectroscopic study, we found that the charge recombination between the conduction band electrons in the TiO 2 film and the electrolyte containing the L-cysteine/L-cystine redox couple is restrained. This journal is © 2012 The Royal Society of Chemistry. Source

Cantoni M.,University of Melbourne | Jonsson U.T.,KTH Royal Institute of Technology | Kao C.-Y.,National Sun Yat - sen University
IEEE Transactions on Automatic Control | Year: 2012

A framework is established for directly accommodating feedback interconnections of unstable distributed-parameter transfer functions in robust stability analysis via integral quadratic constraints (IQCs). This involves transfer function homotopies that are continuous in a ν -gap metric sense. As such, the development includes the extension of ν-gap metric concepts to an irrational setting and the study of uncertainty-set connectedness in these terms. The main IQC based robust stability result is established for constantly-proper transfer functions in the Callier-Desoer algebra; i.e. finitely many unstable poles and a constant limit at infinity. Problems of structured robust stability analysis and robust performance analysis are considered to illustrate use of the main result. Several numerical examples are also presented. These include stability analysis of an autonomous system with uncertain time-delay and a closed-loop control system, accounting for both the gain and phase characteristics of the distributed-parameter uncertainty associated with the nominal rational plant model used for controller synthesis. © 2011 IEEE. Source

Zheng G.,University of Luxembourg | Krikidis I.,University of Cyprus | Ottersten B.,University of Luxembourg | Ottersten B.,KTH Royal Institute of Technology
IEEE Transactions on Wireless Communications | Year: 2013

This paper studies the cooperation between a primary system and a cognitive system in a cellular network where the cognitive base station (CBS) relays the primary signal using amplify-and-forward or decode-and-forward protocols, and in return it can transmit its own cognitive signal. While the commonly used half-duplex (HD) assumption may render the cooperation less efficient due to the two orthogonal channel phases employed, we propose that the CBS can work in a full-duplex (FD) mode to improve the system rate region. The problem of interest is to find the achievable primary-cognitive rate region by studying the cognitive rate maximization problem. For both modes, we explicitly consider the CBS transmit imperfections, which lead to the residual self-interference associated with the FD operation mode. We propose closed-form solutions or efficient algorithms to solve the problem when the related residual interference power is non-scalable or scalable with the transmit power. Furthermore, we propose a simple hybrid scheme to select the HD or FD mode based on zero-forcing criterion, and provide insights on the impact of system parameters. Numerical results illustrate significant performance improvement by using the FD mode and the hybrid scheme. © 2002-2012 IEEE. Source

Franke U.,KTH Royal Institute of Technology
IEEE Transactions on Network and Service Management | Year: 2012

High enterprise IT service availability is a key success factor throughout many industries. While understanding of the economic importance of availability management is becoming more widespread, the implications for management of Service Level Agreements (SLAs) and thinking about availability risk management are just beginning to unfold. This paper offers a framework within which to think about availability management, highlighting the importance of variance of outage costs. The importance of variance is demonstrated using simulations on existing data sets of revenue data. An important implication is that when outage costs are proportional to outage duration, more but shorter outages should be preferred to fewer but longer, in order to minimize variance. Furthermore, two archetypal cases where the cost of an outage depends non-linearly on its duration are considered. An optimal outage length is derived, and some guidance is also given for its application when the variance of hourly downtime costs is considered. The paper is concluded with a discussion about the feasibility of the method, its practitioner relevance and its implications for SLA management. © 2011 IEEE. Source

Katselis D.,KTH Royal Institute of Technology
IEEE Communications Letters | Year: 2012

A fundamental problem in training-based channel estimation for various communication systems is the preamble design. Two crucial aspects in such a design are the achievable mean square error (MSE) and the corresponding peak-to-average power ratio (PAPR). In this letter, preamble-based least squares (LS) channel estimation in CP-OFDM systems is considered. Ignoring the PAPR aspect, several MSE-optimal preambles and a necessary condition for their existence are presented. To this end, a training energy constraint, containing also the energy spent to the cyclic prefix (CP), is imposed. This constraint differs from the usual training energy constraints in the existing literature, which ignore the CP energy during training. These preambles contribute in the completion of existing results concerning MSE-optimal preambles in CP-OFDM systems. However, since high PAPR is an issue concerning these optimal designs, we show how these MSE-optimal preambles can be combined with the usual Zadoff-Chu (ZC) sequences to enlarge the class of PAPR-optimal preambles that achieve good MSE performance at the same time. © 2012 IEEE. Source

Parviainen P.,KTH Royal Institute of Technology | Koivisto M.,Aalto University
Journal of Machine Learning Research | Year: 2013

We consider the problem of finding a directed acyclic graph (DAG) that optimizes a decomposable Bayesian network score. While in a favorable case an optimal DAG can be found in polynomial time, in the worst case the fastest known algorithms rely on dynamic programming across the node subsets, taking time and space 2n, to within a factor polynomial in the number of nodes n. In practice, these algorithms are feasible to networks of at most around 30 nodes, mainly due to the large space requirement. Here, we generalize the dynamic programming approach to enhance its feasibility in three dimensions: first, the user may trade space against time; second, the proposed algorithms easily and efficiently parallelize onto thousands of processors; third, the algorithms can exploit any prior knowledge about the precedence relation on the nodes. Underlying all these results is the key observation that, given a partial order P on the nodes, an optimal DAG compatible with P can be found in time and space roughly proportional to the number of ideals of P, which can be significantly less than 2n. Considering sufficiently many carefully chosen partial orders guarantees that a globally optimal DAG will be found. Aside from the generic scheme, we present and analyze concrete tradeoff schemes based on parallel bucket orders. © 2013 Pekka Parviainen and Mikko Koivisto. Source

Joshi S.K.,University of Oulu | Weeraddana P.C.,KTH Royal Institute of Technology | Codreanu M.,University of Oulu | Latva-Aho M.,University of Oulu
IEEE Transactions on Signal Processing | Year: 2012

The problem of weighted sum-rate maximization (WSRMax) in multicell downlink multiple-input single-output (MISO) systems is considered. The problem is known to be NP-hard. We propose a method, based on branch and bound technique, which solves globally the nonconvex WSRMax problem with an optimality certificate. Specifically, the algorithm computes a sequence of asymptotically tight upper and lower bounds and it terminates when the difference between them falls below a pre-specified tolerance. Novel bounding techniques via conic optimization are introduced and their efficiency is demonstrated by numerical simulations. The proposed method can be used to provide performance benchmarks by back-substituting it into many existing network design problems which relies on WSRMax problem. The method proposed here can be easily extended to maximize any system performance metric that can be expressed as a Lipschitz continuous and increasing function of signal-to-interference-plus-noise ratio. © 2011 IEEE. Source

Holzapfel G.A.,Graz University of Technology | Holzapfel G.A.,KTH Royal Institute of Technology | Ogden R.W.,University of Glasgow
Journal of the Royal Society Interface | Year: 2010

This paper provides the first analysis of the three-dimensional state of residual stress and stretch in an artery wall consisting of three layers (intima, media and adventitia), modelled as a circular cylindrical tube. The analysis is based on experimental results on human aortas with non-atherosclerotic intimal thickening documented in a recent paper by Holzapfel et al. (Holzapfel et al. 2007 Ann. Biomed. Eng. 35, 530-545 (doi:10.1007/s10439-006-9252-z)). The intima is included in the analysis because it has significant thickness and load-bearing capacity, unlike in a young, healthy human aorta. The mathematical model takes account of bending and stretching in both the circumferential and axial directions in each layer of the wall. Previous analysis of residual stress was essentially based on a simple application of the opening-angle method, which cannot accommodate the three-dimensional residual stretch and stress states observed in experiments. The geometry and nonlinear kinematics of the intima, media and adventitia are derived and the associated stress components determined explicitly using the nonlinear theory of elasticity. The theoretical results are then combined with the mean numerical values of the geometrical parameters and material constants from the experiments to illustrate the three-dimensional distributions of the stretches and stresses throughout the wall. The results highlight the compressive nature of the circumferential stress in the intima, which may be associated with buckling of the intima and its delamination from the media, and show that the qualitative features of the stretch and stress distributions in the media and adventitia are unaffected by the presence or absence of the intima. The circumferential residual stress in the intima increases significantly as the associated residual deformation in the intima increases while the corresponding stress in the media (which is compressive at its inner boundary and tensile at its outer boundary) is only slightly affected. The theoretical framework developed herein enables the state of residual stress to be calculated directly, serves to improve insight into the mechanical response of an unloaded artery wall and can be extended to accommodate more general geometries, kinematics and states of residual stress as well as more general constitutive models. © 2009 The Royal Society. Source

Gudnason S.B.,CAS Lanzhou Institute of Modern Physics | Gudnason S.B.,KTH Royal Institute of Technology | Nitta M.,Keio University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

We study a Skyrme-type model with a quadratic potential for a field with S2 vacua. We consider two flavors of the model, the first is the Skyrme model and the second has a sixth-order derivative term instead of the Skyrme term; both with the added quadratic potential. The model contains molecules of half Skyrmions, each of them is a global (anti)monopole with baryon number 1/2. We numerically construct solutions with baryon numbers one through six, and find stable solutions which look like beads on rings. We also construct a molecule with fractional Skyrmions having the baryon numbers 1/3+2/3, by adding a linear potential term. © 2015 American Physical Society. Source

Sorlin S.,KTH Royal Institute of Technology | Sorlin S.,University of Stockholm
Environmental Science and Policy | Year: 2013

This article examines the concepts 'environment' and 'expertise'. It is argued that these concepts, while having long and diverse individual histories, acquired new meaning through a process of mutual co-production which occurred largely in the period 1920-1960, thus significantly preceding the common understanding of environmentalism as a phenomenon emerging in the 1960s. It is further argued that environmental expertise is much predicated on natural science in a range of fields that were integrated into a comprehensive understanding scaling upwards from the local to the global. Quantitative analysis, observing, measuring, and monitoring rates of change of a growing set of indicators were other key features of this emerging understanding of the environmental. Yet another key aspect was the self-proclaimed ability of environmental expertise to predict rates and directions of current and, crucially, future changes of global environmental conditions, increasingly assuming that these changes were largely of human origin. In addition to thus presenting a brief history of environmental expertise the article also makes the point that the environmental was, despite changed by human action, essentially regarded as something that did not in itself belong to the human or the social and thus the implicit prerogative of the natural sciences. The article argues, on the contrary, that there is solid historical evidence to suggest that 'environment' should also, perhaps primarily, be understood as a social concept, or rather as an extension of the social into nature. As conventional environmental expertise has failed to provide the advice needed to question the driving forces behind environmental degradation and lack of sustainability it is here instead suggested that environmental expertise be fundamentally reconfigured to include the social sciences and humanities, and that concerted research efforts are directed to the understanding of the formation of environmental expertise. © 2013. Source

Koivisto T.S.,KTH Royal Institute of Technology | Urban F.R.,Free University of Colombia
Journal of Cosmology and Astroparticle Physics | Year: 2015

The Maxwell action is conformally invariant and classically ignorant of conformally flat metrics. However, if the vector lives in a disformal metric - as it does if residing upon a moving brane - this is no longer true. The disformal coupling is then mediated by a Dirac-Born-Infeld scalar field. Here a systematic dynamical system analysis is developed for anisotropic Bianchi I cosmology with a massive disformally coupled vector field. Several new fixed points are found, including anisotropic scaling solutions. The formalism here presented can be conveniently applied to general scenarios with or without extra dimensional motivations. This is illustrated here by performing a complete analysis with the assumption that both the potentials and the warp factor for the brane are (nearly) exponential. In that case, the anisotropic fixed points are either not attractors, do not describe accelerating expansion or else they feature too large anisotropies to be compatible with observations. Nonetheless, viable classes of models exist where isotropy is retained due to rapid oscillations of the vector field, thus providing a possible realisation of disformally interacting massive dark matter. © 2015 IOP Publishing Ltd and Sissa Medialab srl . Source

Lindborg P.,Nanyang Technological University | Lindborg P.,KTH Royal Institute of Technology
Applied Acoustics | Year: 2015

Sound is a multi-faceted phenomenon and a critical modality in all kinds of sevicescapes. At restaurants, our senses are intensively stimulated. They are social places that depend on acoustic design for their success. Considering the large economic interests, surprisingly little empirical research on the psychoacoustics of restaurants is available. Contributing to theory building, this article proposes a typology of designed and non-designed sonic elements in restaurants. Results from a survey of 112 restaurants in Singapore are presented, with a focus on one element of the typology, namely interior design materials. The collected data included on-site sound level, audio recordings from which psychoacoustic descriptors such as Loudness and Sharpness were calculated, perceptual ratings using the Swedish Soundscape Quality protocol, and annotations of physical features such as Occupancy. We have introduced a measure, Priciness, to compare menu cost levels between the surveyed restaurants. Correlation analysis revealed several patterns: for example, that Priciness was negatively correlated with Loudness. Analysis of annotations of interior design materials supported a classification of the restaurants in categories of Design Style and Food Style. These were investigated with MANOVA, revealing significant differences in psychoacoustic, physical, and perceptual features between categories among the surveyed restaurants: for example, that restaurants serving Chinese food had the highest prevalence of stone materials, and that Western-menu places were the least loud. Some implications for managers, acoustic designers, and researchers are discussed. © 2015 Elsevier Ltd. All rights reserved. Source

O'Reilly C.J.,KTH Royal Institute of Technology
Applied Acoustics | Year: 2015

Acoustic liners are used extensively in engineering applications, particularly in aero-engines and automotive exhaust systems. In this paper, a flow impedance boundary conditions is introduced into the wave expansion method with the aim of providing an efficient methodology for computing the acoustic propagation through a lined duct with flow. For a potential flow, the boundary layer and the lined wall are included in the discretisation scheme by the Myers flow impedance boundary condition. The acoustic propagation through a flow impedance tube is computed in order to validate the implementation of the impedance boundary condition in this scheme. The results show that this computationally light methodology provides generally good agreement with the experimental data. © 2014 Elsevier Ltd. All rights reserved. Source

Jebari K.,KTH Royal Institute of Technology
Neuroethics | Year: 2013

Brain machine interface (BMI) technology makes direct communication between the brain and a machine possible by means of electrodes. This paper reviews the existing and emerging technologies in this field and offers a systematic inquiry into the relevant ethical problems that are likely to emerge in the following decades. © 2013 Springer Science+Business Media Dordrecht. Source

Heisenberg L.,KTH Royal Institute of Technology | Heisenberg L.,The Oskar Klein Center
Journal of Cosmology and Astroparticle Physics | Year: 2015

In this work we study the theory of extended quasidilaton massive gravity together with the presence of matter fields. After discussing the homogeneous and isotropic fully dynamical background equations, which governs the exact expansion history of the universe, we consider small cosmological perturbations around these general FLRW solutions. The stability of tensor, vector and scalar perturbations on top of these general background solutions give rise to slightly different constraints on the parameters of the theory than those obtained in the approximative assumption of the late-time asymptotic form of the expansion history, which does not correspond to our current epoch. This opens up the possibility of stable FLRW solutions to be compared with current data on cosmic expansion with the restricted parameter space based on theoretical ground. Source

Ong Y.C.,KTH Royal Institute of Technology
Journal of Cosmology and Astroparticle Physics | Year: 2015

Christodoulou and Rovelli have shown that black holes have large interiors that grow asymptotically linearly in advanced time, and speculated that this may be relevant to the information loss paradox. We show that there is no simple relation between the interior volume of an arbitrary black hole and its horizon area. That is, the volume enclosed is not necessarily a monotonically increasing function of the surface area. © 2015 IOP Publishing Ltd and Sissa Medialab srl. Source

Qi C.,KTH Royal Institute of Technology
Journal of Physics G: Nuclear and Particle Physics | Year: 2015

It is becoming increasingly important to understand the uncertainties of nuclear mass model calculations and their limitations when extrapolating to driplines. In this paper we evaluate the parameter uncertainties of the Duflo-Zuker (DZ) shell model mass formulae by fitting to the latest experimental mass compilation AME2012 using the least square and minimax fitting procedures. We also analyze the propagation of the uncertainties in binding energy calculations when extrapolated to driplines. The parameter uncertainties and uncertain propagations are evaluated with the help of the covariance matrix thus derived. Large deviations from the extrapolations of AME2012 are seen in superheavy nuclei. A simplified version of the DZ model (DZ19) with much smaller uncertainties than that of DZ33 is proposed. Calculations are compared with results from other mass formulae. Systematics on the uncertainty propagation as well as the positions of the driplines are also presented. The DZ mass formulae are shown to be well defined with good extrapolation properties and rather small uncertainties, even though some of the parameters of the full DZ33 model cannot be fully determined by fitting to available experimental data. © 2015 IOP Publishing Ltd. Source

Burgess J.M.,The Oskar Klein Center | Burgess J.M.,KTH Royal Institute of Technology
Monthly Notices of the Royal Astronomical Society | Year: 2014

The understanding of the prompt γ-ray spectra of gamma-ray bursts (GRBs) is of great importance to correctly interpret the physical mechanisms that produce the underlying event as well as the structure of the relativistic jet from which the emission emanates. Time-resolved analysis of these spectra is the main method of extracting information from the data. In this work, several techniques for temporal binning of GRB spectra are examined to understand the systematics associated with each with the goal of finding the best method(s) to bin light curves for analysis. The following binning methods are examined: constant cadence (CC), Bayesian blocks (BBs), signal-to-noise (S/N) and Knuth bins (KB). I find that both the KB and BB methods reconstruct the intrinsic spectral evolution accurately while the S/N method fails in most cases. The CC method is accurate when the cadence is not too coarse but does not necessarily bin the data based on the true source variability. Additionally, the integrated pulse properties are investigated and compared to the time-resolved properties. If intrinsic spectral evolution is present, then the integrated properties are not useful in identifying physical and cosmological properties of GRBs without knowing the physical emission mechanism and its evolution. © 2014 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Edvardsson Bjornberg K.,KTH Royal Institute of Technology
Energy Policy | Year: 2013

The overall goal of the UNFCCC is to prevent dangerous anthropogenic interference with the climate system. In policy practice, this goal is mainly operationalized through three types of mitigation targets: emission, atmospheric concentration and temperature targets. The typical function of climate mitigation goals is to regulate action towards goal achievement. This is done in several ways. Mitigation goals help the structuring of the greenhouse gas (GHG) abatement action, over time and between agents; they constitute a standard against which GHG abatement can be assessed and evaluated; they motivate climate conscious behavior; and discourage defection from cooperative abatement regimes. Although the three targets clearly relate to one another, there could be differences in how well they fulfill these functions. In this article, the effectiveness of emission, concentration and temperature targets in guiding and motivating action towards the UNFCCC's overall aim is analyzed using a framework for rational goal evaluation developed by Edvardsson and Hansson (2005) as an analytical tool. It is argued that to regulate action effectively, mitigation goals should ideally satisfy four criteria: precision, evaluability, attainability and motivity. Only then can the target fulfill its typical function, i.e., to guide and motivate action in a way that facilitates goal achievement. © 2013 Elsevier Ltd. Source

Alpcan T.,TU Berlin | Buchegger S.,KTH Royal Institute of Technology
IEEE Transactions on Mobile Computing | Year: 2011

Vehicular networks (VANETs) can be used to improve transportation security, reliability, and management. This paper investigates security aspects of VANETs within a game-theoretic framework where defensive measures are optimized with respect to threats posed by malicious attackers. The formulations are chosen to be abstract on purpose in order to maximize applicability of the models and solutions to future systems. The security games proposed for vehicular networks take as an input centrality measures computed by mapping the centrality values of the car networks to the underlying road topology. The resulting strategies help locating most valuable or vulnerable points (e.g., against jamming) in vehicular networks. Thus, optimal deployment of traffic control and security infrastructure is investigated both in the static (e.g., fixed roadside units) and dynamic cases (e.g., mobile law enforcement units). Multiple types of security games are studied under varying information availability assumptions for the players, leading to fuzzy game and fictitious play formulations in addition to classical zero-sum games. The effectiveness of the security game solutions is evaluated numerically using realistic simulation data obtained from traffic engineering systems. © 2011 IEEE. Source

Baard P.,KTH Royal Institute of Technology
Journal of Risk Research | Year: 2014

Social decision-making involving risks ideally results in obligations to avoid expected harms or keep them within acceptable limits. Ambitious goals aimed at avoiding or greatly reducing risks might not be feasible, forcing the acceptance of higher degrees of risk (i.e. unrealistic levels of risk reduction are revised to comport with beliefs regarding abilities). In this paper, the philosophical principle ‘ought implies can’ is applied to the management of complex risks, exemplified by the risks associated with climate change. In its common interpretation, the principle states that we cannot expect an agent to perform something that lies beyond his or her abilities. However, it is here argued that this principle requires setting thresholds for legitimate claims of inabilities that justify the waiving of normative demands. This paper discuss three claims: (1) that caution is required before revising a risk-reducing goal that is perhaps exceedingly ambitious; (2) that claims on abilities are not only descriptive, but also value-laden; and (3) that the function of a goal has to be clarified before risk-reducing goals are revised. Risk-reducing goals that initially seem unrealistic arguably serve performance-enhancing purposes in risk management. Neglecting such goals could lead to choosing less desirable, but certainly feasible, risk-reducing goals. © 2014 Taylor & Francis Source

Moberg C.,KTH Royal Institute of Technology
Pure and Applied Chemistry | Year: 2016

In enantioselective reactions, the major, desired enantiomer is commonly obtained along with the minor, undesired enantiomer. By continuous recycling of this undesired enantiomer back to starting material, products with improved enantiomeric purity can be obtained. Such in situ minor enantiomer recycling can be accomplished by coupling the catalytic reaction to an exergonic transformation of a sacrificial reagent. The method has been applied to the synthesis of O-acylated cyanohydrins, which serve as starting materials for a variety of biologically active compounds. © 2016 IUPAC & De Gruyter. Source

Gattami A.,Massachusetts Institute of Technology | Gattami A.,KTH Royal Institute of Technology
IEEE Transactions on Automatic Control | Year: 2010

We consider the problem of stochastic finite- and infinite-horizon linear quadratic control under power constraints. The calculations of the optimal control law can be done off-line as in the classical linear quadratic Gaussian control theory using dynamic programming, which turns out to be a special case of the new theory developed in this technical note. A numerical example is solved using the new methods. © 2009 IEEE. Source

Radon, radium and helium data from three sites in granitic rock in Sweden (Forsmark and Laxemar) and Finland (Olkiluoto) from depths greater than 1,000 m were interpreted by a model that describes how daughter nuclides, including helium from uranium and thorium decay, escape from minerals, enter the pore water in the rock matrix and diffuse to the seeping water in the fractures in the rock. The radium concentrations are on the order of <30 Bq/l of water that has recently infiltrated and then emerged from the rock. Radon concentrations are mostly several orders of magnitude larger. The model predicts values in the same range. The fair agreement between model results, field data and laboratory data over a scale spanning micrometres over meters to kilometres, and time scales of days to millions of years, shows that the micropores of the rock matrix are connected even at depths down to and beyond a kilometre. Molecular diffusion in the matrix pore water is a key migration mechanism. Laboratory-derived sorption coefficients for radium are of the same magnitude as those needed in the modelling of the in situ data to give good agreement. © 2013 Springer-Verlag Berlin Heidelberg. Source

Olsson J.,Lund University | Ryden T.,KTH Royal Institute of Technology
IEEE Transactions on Signal Processing | Year: 2011

Smoothing in state-space models amounts to computing the conditional distribution of the latent state trajectory, given observations, or expectations of functionals of the state trajectory with respect to this distribution. In recent years there has been an increased interest in Monte Carlo-based methods, often involving particle filters, for approximate smoothing in nonlinear and/or non-Gaussian state-space models. One such method is to approximate filter distributions using a particle filter and then to simulate, using backward kernels, a state trajectory backwards on the set of particles. We show that by simulating multiple realizations of the particle filter and adding a Metropolis-Hastings step, one obtains a Markov chain Monte Carlo scheme whose stationary distribution is the exact smoothing distribution. This procedure expands upon a similar one recently proposed by Andrieu, Doucet, Holenstein, and Whiteley. We also show that simulating multiple trajectories from each realization of the particle filter can be beneficial from a perspective of variance versus computation time, and illustrate this idea using two examples. © 2011 IEEE. Source

Larsson P.-L.,KTH Royal Institute of Technology
Materials and Design | Year: 2011

The correlation between residual stresses and the global properties, i.e. hardness and size of the contact area, given by a sharp indentation test have been studied quite frequently in recent years. The investigations presented have been based on experimental, theoretical and numerical methods and as a result, the basic features of the problem are now well understood. Furthermore, in this context quantitative relations, for the determination of residual stresses using sharp indentation, have been presented. Such relations have proven to be reliable in case of predominantly tensile residual stresses while the accuracy of predictions is much worse at compressive stress states. It is therefore the aim of the present study to investigate this matter in some detail and to present possible mechanisms for the difference in indentation behavior between tension and compression. Accordingly, the results are essentially qualitative but necessary and detailed investigations needed for a quantitative understanding are suggested. The present analysis is based on theoretical and numerical methods and in the latter case, the finite element method (FEM) is relied upon. Classical Mises elastoplastic material behavior is assumed throughout the investigation. © 2010 Elsevier Ltd. Source

Kroon M.,KTH Royal Institute of Technology
Engineering Fracture Mechanics | Year: 2011

Asymptotic analyses of the mechanical fields in front of stationary and propagating cracks are important for several reasons. For example, they facilitate the understanding of the mechanical and physical state in front of crack tips, and they enable prediction of crack growth. Furthermore, efficient modelling of arbitrary crack growth by use of XFEM (extended finite element method) requires accurate knowledge of the asymptotic crack tip fields. The present study focuses on the asymptotic fields in front of a crack that propagates dynamically in rubber. Static analyses of this type of problem have been made in previous studies. In order to be able to compare the present results with these earlier studies, the constitutive model from Knowles and Sternberg (J. Elast. 3:67-107, 1973) was adopted. It is assumed that viscoelastic stresses become negligible compared with the singular elastic stresses close to the crack tip. The present analysis shows that in materials with a significant hardening, the inertia term in the equations of motion becomes negligible in the asymptotic analysis. However, for a neoHookean type of model, inertia comes into play and causes a maximum theoretical crack speed that equals the shear wave speed. © 2011 Elsevier Ltd. Source

Schenk L.,KTH Royal Institute of Technology
International Journal of Occupational and Environmental Health | Year: 2010

It has previously been shown that occupational exposure limits (OELs) for the same substance can vary significantly between different standard-setters. The work presented in this paper identifies the steps in the process towards establishing an OEL and how variations in those processes could account for these differences. This study selects for further scrutiny substances for which the level of OELs vary by a factor of 100, focussing on 45 documents concerning 14 substances from eight standard-setters. Several of the OELs studied were more than 20 years old and based on outdated knowledge. Furthermore, different standard-setters sometimes based their OELs on different sets of data, and data availability alone could not explain all differences in the selection of data sets used by standard-setters. While the interpretation of key studies did not differ significantly in standard-setters' documentations, the evaluations of the key studies' quality did. Also, differences concerning the critical effect coincided with differences in the level of OELs for half of the substances. Source

Wilde M.W.,AF Industry AB | Johansson F.,KTH Royal Institute of Technology
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2013

Structural reliability analysis is not widely used for the design and assessment of concrete dams. In this paper, the system reliability of a spillway structure consisting of two monoliths is calculated. Limit state functions are defined from the failure modes sliding in the concrete rock contact, sliding in the rock mass, and adjusted overturning. Random variables in the limit state functions are defined by stochastic distributions. These are defined based on site investigations and laboratory tests from samples taken at the dam. Simulations and information from the literature are used for the remaining variables. The safety index is calculated by the first-order reliability method for each failure mode and monolith, and the system reliability is approximated by direct integration of the bivariate normal distribution. The output is the safety index including associated sensitivity values at the single failure mode, monolith, and system levels. The results show that the system safety is governed by a persistent rock joint beneath one monolith. A system reliability analysis is found to be a useful tool in the dam risk management process as it can be used to calculate the probability of failure and to identify important failure modes and variables. © 2013 American Society of Civil Engineers. Source

Holm H.,KTH Royal Institute of Technology
Proceedings of the Annual Hawaii International Conference on System Sciences | Year: 2014

A frequent claim that has not been validated is that signature based network intrusion detection systems (SNIDS) cannot detect zero-day attacks. This paper studies this property by testing 356 severe attacks on the SNIDS Snort, configured with an old official rule set. Of these attacks, 183 attacks are zero-days' to the rule set and 173 attacks are theoretically known to it. The results from the study show that Snort clearly is able to detect zero-days' (a mean of 17% detection). The detection rate is however on overall greater for theoretically known attacks (a mean of 54% detection). The paper then investigates how the zero-days' are detected, how prone the corresponding signatures are to false alarms, and how easily they can be evaded. Analyses of these aspects suggest that a conservative estimate on zero-day detection by Snort is 8.2%. © 2014 IEEE. Source

Zhang L.,ABB | Harnefors L.,ABB | Nee H.-P.,KTH Royal Institute of Technology
IEEE Transactions on Power Systems | Year: 2011

In this paper, voltage-source converter (VSC) based high-voltage dc (HVDC) transmission is investigated for interconnection of two very weak ac systems. By using the recently proposed power-synchronization control, the short-circuit capacities of the ac systems are no longer the limiting factors, but rather the load angles. For the analysis of the stability, the Jacobian transfer matrix concept has been introduced. The right-half plane (RHP) transmission zero of the ac Jacobian transfer matrix moves closer to the origin with larger load angles. The paper shows that, due to the bandwidth limitation imposed by the RHP zero on the direct-voltage control of the VSC, high dc-capacitance values are needed for such applications. In addition, the paper proposes a control structure particularly designed for weak-ac-system interconnections. As an example, it is shown that the proposed control structure enables a power transmission of 0.86 p.u. from a system with the short-circuit ratio (SCR) of 1.2 to a system with an SCR of 1.0. This should be compared to previous results for VSC based HVDC using vector current control. In this case, only 0.4 p.u. power transmission can be achieved for dc link where only one of the ac systems has an SCR of 1.0. © 2010 IEEE. Source

Zetterberg P.,KTH Royal Institute of Technology
Eurasip Journal on Advances in Signal Processing | Year: 2011

We describe an implementation of TDD reciprocity based zero-forcing linear precoding on a wireless testbed. A calibration technique which self-calibrates the base-station without the need for help from other nodes is described. Performance results in terms of downlink channel estimation error as well as bit error rate (BER) and signal to interference noise and distortion ratio (SINDR) are presented for a scenario with two base-stations and two mobile stations, with two antennas at the base-stations and a single antenna at the mobile-station. The results show considerable performance improvements over reference schemes (such as maximum ratio transmission). However, our analysis also reveals that the hardware impairments significantly limit the performance achieved. We further investigate how to model these impairments and attempt to predict the SINDR, such as what would be needed in a coordinated multipoint (CoMP) scenario where scheduling is performed jointly over the two cells. Although the results are obtained for a MISO scenario the general conclusions are relevant also for MIMO scenarios. Copyright © 2011 Per Zetterberg. Source

Schmid P.J.,Imperial College London | Brandt L.,KTH Royal Institute of Technology
Applied Mechanics Reviews | Year: 2014

This article presents techniques for the analysis of fluid systems. It adopts an optimization-based point of view, formulating common concepts such as stability and receptivity in terms of a cost functional to be optimized subject to constraints given by the governing equations. This approach differs significantly from eigenvalue-based methods that cover the time-asymptotic limit for stability problems or the resonant limit for receptivity problems. Formal substitution of the solution operator for linear time-invariant systems results in the matrix exponential norm and the resolvent norm as measures to assess the optimal response to initial conditions or external harmonic forcing. The optimization-based approach can be extended by introducing adjoint variables that enforce governing equations and constraints. This step allows the analysis of far more general fluid systems, such as time-varying and nonlinear flows, and the investigation of wavemaker regions, structural sensitivities, and passive control strategies. Copyright © 2014 by ASME. Source

Leurent S.,Imperial College London | Volin D.,KTH Royal Institute of Technology | Volin D.,NASU Bogolyubov Institute for Theoretical Physics
Nuclear Physics B | Year: 2013

Using the FiNLIE solution of the AdS/CFT Y-system, we compute the anomalous dimension of the Konishi operator in planar N=4 SYM up to eight loops, i.e. up to the leading double wrapping order. At this order a non-reducible Euler-Zagier sum, ζ1,2,8, appears for the first time. We find that at all orders in perturbation, every spectral-dependent quantity of the Y-system is expressed through multiple Hurwitz zeta functions, hence we provide a Mathematica package to manipulate these functions, including the particular case of Euler-Zagier sums. Furthermore, we conjecture that only Euler-Zagier sums can appear in the answer for the anomalous dimension at any order in perturbation theory.We also resum the leading transcendentality terms of the anomalous dimension at all orders, obtaining a simple result in terms of Bessel functions. Finally, we demonstrate that exact Bethe equations should be related to an absence of poles condition that becomes especially non-trivial at double wrapping. © 2013 Elsevier B.V. Source

Huang L.,KTH Royal Institute of Technology | Mao X.,University of Strathclyde
IEEE Transactions on Automatic Control | Year: 2011

In recent years, singular hybrid systems have received considerable attention. However, few results are concerned with stability of singular hybrid stochastic systems. Based on a stability result for singular hybrid systems, this note studies mean-square stability of singular hybrid stochastic systems. It is found that the diffusions and the Markov chain may play important roles in system analysis in mean-square sense. As a special case, a criterion for mean-square stability of hybrid stochastic systems is developed by the frequency domain approach. © 2006 IEEE. Source

Wang M.,Dalian University of Technology | Han K.,Dalian University of Technology | Zhang S.,Dalian University of Technology | Sun L.,Dalian University of Technology | Sun L.,KTH Royal Institute of Technology
Coordination Chemistry Reviews | Year: 2015

The development of energy-efficient, cost-effective and durable photocatalytic systems for water splitting is one of the scientific problems that must be solved before the successful transformation from a fossil fuel-based economy to a solar fuel-based economy can be realized. Conventional photocatalytic systems are generally divided into heterogeneous systems of semiconductors, usually modified by noble metals or inorganic cocatalysts, and homogeneous systems comprised of molecular catalysts and organic or organometallic chromophores. In recent years, some hybrid photocatalytic systems were reported to be highly active and robust for photoinduced H2 production, indicating that the integration of semiconducting materials with proper molecular catalysts is an effective strategy for constructing efficient photocatalytic systems for water splitting. This review will focus on hybrid photocatalytic systems, developed in the past three years, in which proton reduction molecular catalysts incorporate either semiconducting materials or inorganic, metal-organic, and other polymeric nanomaterials for photochemical H2 generation from water. In the last section of the review, problems existing in the current hybrid photocatalytic systems are discussed; future challenges and developments are envisaged. © 2014 Elsevier B.V. Source

Pe'er A.,US Space Telescope Science Institute | Pe'er A.,Harvard - Smithsonian Center for Astrophysics | Ryde F.,KTH Royal Institute of Technology
Astrophysical Journal | Year: 2011

We consider the emission of photons from the inner parts of a relativistically expanding plasma outflow, characterized by a constant Lorentz factor, Γ. Photons that are injected in regions of high optical depth are advected with the flow until they escape at the photosphere. Due to multiple scattering below the photosphere, the locally emerging comoving photon distribution is thermal. However, as an observer simultaneously sees photons emitted from different angles, hence with different Doppler boosting, the observed spectrum is a multicolor blackbody. We calculate here the properties of the observed spectrum at different observed times. Due to the strong dependence of the photospheric radius on the angle to the line of sight, for parameters characterizing gamma-ray bursts (GRBs) thermal photons are seen up to tens of seconds following the termination of the inner engine. At late times, following the inner engine termination, both the number flux and energy flux of the thermal spectrum decay as Ft -2. At these times, the multicolor blackbody emission results in a power law at low energies (below the thermal peak), with power-law index Fνν0. We discuss the implications and limitations of this result in the study of GRBs. © 2011. The American Astronomical Society. All rights reserved. Source

Briat C.,KTH Royal Institute of Technology
IEEE Transactions on Automatic Control | Year: 2011

The Jensen's inequality plays a crucial role in the analysis of time-delay and sampled-data systems. Its conservatism is studied through the use of the Grüss Inequality. It has been reported in the literature that fragmentation (or partitioning) schemes allow to empirically improve the results. We prove here that the Jensen's gap can be made arbitrarily small provided that the order of uniform fragmentation is chosen sufficiently large. Nonuniform fragmentation schemes are also shown to speed up the convergence in certain cases. Finally, a family of bounds is characterized and a comparison with other bounds of the literature is provided. It is shown that the other bounds are equivalent to Jensen's and that they exhibit interesting well-posedness and linearity properties which can be exploited to obtain better numerical results. © 2011 IEEE. Source

Sandberg H.,KTH Royal Institute of Technology | Delvenne J.-C.,University of Namur | Doyle J.C.,California Institute of Technology
IEEE Transactions on Automatic Control | Year: 2011

In this paper, we take a control-theoretic approach to answering some standard questions in statistical mechanics, and use the results to derive limitations of classical measurements. A central problem is the relation between systems which appear macroscopically dissipative but are microscopically lossless. We show that a linear system is dissipative if, and only if, it can be approximated by a linear lossless system over arbitrarily long time intervals. Hence lossless systems are in this sense dense in dissipative systems. A linear active system can be approximated by a nonlinear lossless system that is charged with initial energy. As a by-product, we obtain mechanisms explaining the Onsager relations from time-reversible lossless approximations, and the fluctuation-dissipation theorem from uncertainty in the initial state of the lossless system. The results are applied to measurement devices and are used to quantify limits on the so-called observer effect, also called back action, which is the impact the measurement device has on the observed system. In particular, it is shown that deterministic back action can be compensated by using active elements, whereas stochastic back action is unavoidable and depends on the temperature of the measurement device. © 2006 IEEE. Source

Chen G.,State University of New York at Buffalo | Chen G.,Harbin Institute of Technology | Agren H.,KTH Royal Institute of Technology | Ohulchanskyy T.Y.,State University of New York at Buffalo | And 2 more authors.
Chemical Society Reviews | Year: 2015

Light upconverting nanostructures employing lanthanide ions constitute an emerging research field recognized with wide ramifications and impact in many areas ranging from healthcare, to energy and, to security. The core-shell design of these nanostructures allows us to deliberately introduce a hierarchy of electronic energy states, thus providing unprecedented opportunities to manipulate the electronic excitation, energy transfer and upconverted emissions. The core-shell morphology also causes the suppression of quenching mechanisms to produce efficient upconversion emission for biophotonic and photonic applications. Using hierarchical architect, whereby each shell layer can be defined to have a specific feature, the electronic structure as well as the physiochemical structure of the upconverting nanomaterials can be tuned to couple other electronic states on the surface such as excitations of organic dye molecules or localized surface plasmons from metallic nanostructures, or to introduce a broad range of imaging or therapeutic modalities into a single conduct. In this review, we summarize the key aspects of nanophotonic control of the light upconverting nanoparticles through governed design and preparation of hierarchical shells in the core-shell nanostructures, and review their emerging applications in the biomedical field, solar energy conversion, as well as security encoding. This journal is © The Royal Society of Chemistry. Source

Yu Z.,Dalian University of Technology | Li F.,Dalian University of Technology | Sun L.,Dalian University of Technology | Sun L.,KTH Royal Institute of Technology
Energy and Environmental Science | Year: 2015

Conceptually new research on dye-sensitized photoelectrochemical cells (DS-PECs), through which solar-driven water splitting to generate solar fuel in the form of hydrogen is realized, has attracted growing interest in the past few years. DS-PECs are based on the configurations of dye-sensitized solar cells (DSCs), but with an aim to drive the two half reactions of water splitting at physically separated two compartments (electrodes) rather than to generate electrical power. Herein, we review some of the recent advances in the design and construction of functional DS-PECs for visible light-driven water splitting together with some comments on the performance of these devices. Future challenges towards the development of more efficient dye-sensitized photoelectrochemical devices are addressed in the end. © 2015 The Royal Society of Chemistry. Source

Boano F.,Polytechnic University of Turin | Harvey J.W.,U.S. Geological Survey | Marion A.,University of Padua | Packman A.I.,Northwestern University | And 3 more authors.
Reviews of Geophysics | Year: 2014

Fifty years of hyporheic zone research have shown the important role played by the hyporheic zone as an interface between groundwater and surface waters. However, it is only in the last two decades that what began as an empirical science has become a mechanistic science devoted to modeling studies of the complex fluid dynamical and biogeochemical mechanisms occurring in the hyporheic zone. These efforts have led to the picture of surface-subsurface water interactions as regulators of the form and function of fluvial ecosystems. Rather than being isolated systems, surface water bodies continuously interact with the subsurface. Exploration of hyporheic zone processes has led to a new appreciation of their wide reaching consequences for water quality and stream ecology. Modern research aims toward a unified approach, in which processes occurring in the hyporheic zone are key elements for the appreciation, management, and restoration of the whole river environment. In this unifying context, this review summarizes results from modeling studies and field observations about flow and transport processes in the hyporheic zone and describes the theories proposed in hydrology and fluid dynamics developed to quantitatively model and predict the hyporheic transport of water, heat, and dissolved and suspended compounds from sediment grain scale up to the watershed scale. The implications of these processes for stream biogeochemistry and ecology are also discussed. ©2014. American Geophysical Union. All Rights Reserved. Source

He S.,Zhejiang University | He S.,KTH Royal Institute of Technology | Zhang X.,Zhejiang University | He Y.,Zhejiang University
Optics Express | Year: 2013

Electronics circuits keep shrinking in dimensions, as requested by Moore's law. In contrast, photonic waveguides and circuit elements still have lateral dimensions on the order of the wavelength. A key to make photonics have a microelectronics-like development is a drastic reduction of size. To achieve this, we need a low-loss nanoscale waveguide with a drastically reduced mode area and an ultra-high effective refractive index. For this purpose, we propose here several low-loss waveguide structures based on graphene nano-ribbons. An extremely small mode area (∼10-7λ0 2, one order smaller than the smallest mode area of any waveguide that has ever been reported in the literature; here λ0 is the operating wavelength in vacuum) and an extremely large effective refractive index (several hundreds) are achieved. As a device example, a nano-ring cavity of ultrasmall size (with a diameter of ∼10-2λ0) is designed. Our study paves the way for future VLSI (very-large-scale integration) optoelectronics. © 2013 Optical Society of America. Source

Zhang L.,ABB | Harnefors L.,ABB | Nee H.-P.,KTH Royal Institute of Technology
IEEE Transactions on Power Systems | Year: 2010

In this paper, a novel control method of grid-connected voltage-source converters (VSCs) is proposed. The method can be generally applied for all grid-connected VSCs but may be of most importance in high-voltage dc (HVDC) applications. Different from the previous control methods, the proposed method utilizes the internal synchronization mechanism in ac systems, in principle, similar to the operation of a synchronous machine. By using this type of power-synchronization control, the VSC avoids the instability caused by a standard phase-locked loop in a weak ac-system connection. Moreover, a VSC terminal can give the weak ac system strong voltage support, just like a normal synchronous machine does. The control method is verified by both analytical models and time simulations. © 2010 IEEE. Source

Levihn F.,KTH Royal Institute of Technology
Energy | Year: 2014

CO2 abatement and the transition to sustainable energy systems are of great concern, calling for investments in both old and new technologies. There are many perspectives on how to account for these emissions, not least when it comes to how the roles of different alternative energy production options should be emphasized. Confusion and conflicting interests regarding the appropriate accounting methods for allocating CO2 emissions interfere with effective energy policy and the efficient use of corporate and national resources. Possible investments in the Stockholm district heating network and how they interact with the electric power grid illustrate the influence of different accounting methods on alternative energy production options. The results indicate that, for several abatement options, performance in terms of reduced CO2 emissions might be either improved or degraded depending on whether or how alternative electricity production is accounted for. The results provide guidelines for whether, how, and when different allocation methods are appropriate, guidelines relevant to academia, industrial leaders, and policymakers in multiple areas related to power production and consumption. © 2014 Elsevier Ltd. Source

Bjorkman B.,KTH Royal Institute of Technology
Journal of Pragmatics | Year: 2011

This paper will report the findings of a study that has investigated spoken English as a lingua franca (ELF) usage in Swedish higher education. The material comprises digital recordings of lectures and student group-work sessions, all being naturally occurring, authentic high-stakes spoken exchange, i.e. from non-language-teaching contexts. The aim of the present paper, which constitutes a part of a larger study, has been to investigate the role pragmatic strategies play in the communicative effectiveness of English as a lingua franca. The paper will document types of pragmatic strategies as well as point to important differences between the two speech event types and the implications of these differences for English-medium education. The findings show that lecturers in ELF settings make less frequent use of pragmatic strategies than students who deploy these strategies frequently in group-work sessions. Earlier stages of the present study (Björkman, 2008a, 2008b, 2009) showed that despite frequent non-standardness in the morphosyntax level, there is little overt disturbance in student group-work, and it is highly likely that a variety of pragmatic strategies that students deploy prevents some disturbance. It is reasonable to assume that, in the absence of appropriate pragmatic strategies used often in lectures, there is an increased risk for covert disturbance. © 2010 Elsevier B.V. Source

Muduli P.K.,Gothenburg University | Heinonen O.G.,Argonne National Laboratory | Heinonen O.G.,Northwestern University | Akerman J.,Gothenburg University | Akerman J.,KTH Royal Institute of Technology
Physical Review Letters | Year: 2012

We discuss the coherence of magnetic oscillations in a magnetic tunnel junction based spin torque oscillator as a function of the external field angle. Time-frequency analysis shows mode hopping between distinct oscillator modes, which arises from linear and nonlinear couplings in the Landau-Lifshitz-Gilbert equation, analogous to mode hopping observed in semiconductor ring lasers. These couplings and, therefore, mode hopping are minimized near the current threshold for the antiparallel alignment of free-layer with reference layer magnetization. Away from the antiparallel alignment, mode hopping limits oscillator coherence. © 2012 American Physical Society. Source

Jalden J.,KTH Royal Institute of Technology | Elia P.,Eurecom
IEEE Transactions on Information Theory | Year: 2012

In the setting of quasi-static multiple-input multiple-output channels, we consider the high signal-to-noise ratio (SNR) asymptotic complexity required by the sphere decoding (SD) algorithm for decoding a large class of full-rate linear space-time codes. With SD complexity having random fluctuations induced by the random channel, noise, and codeword realizations, the introduced SD complexity exponent manages to concisely describe the computational reserves required by the SD algorithm to achieve arbitrarily close to optimal decoding performance. Bounds and exact expressions for the SD complexity exponent are obtained for the decoding of large families of codes with arbitrary performance characteristics. For the particular example of decoding the recently introduced threaded cyclic-division-algebra-based codes - the only currently known explicit designs that are uniformly optimal with respect to the diversity multiplexing tradeoff - the SD complexity exponent is shown to take a particularly concise form as a non-monotonic function of the multiplexing gain. To date, the SD complexity exponent also describes the minimum known complexity of any decoder that can provably achieve a gap to maximum likelihood performance that vanishes in the high SNR limit. © 2012 IEEE. Source

Hellman O.,Linkoping University | Skorodumova N.V.,KTH Royal Institute of Technology | Skorodumova N.V.,Uppsala University | Simak S.I.,Linkoping University
Physical Review Letters | Year: 2012

Charge redistribution at low oxygen vacancy concentrations in ceria have been studied in the framework of the density functional theory. We propose a model to approach the dilute limit using the results of supercell calculations. It allows one to reproduce the characteristic experimentally observed behavior of composition versus oxygen pressure dependency. We show that in the dilute limit the charge redistribution is likely to be driven by a mechanism different from the one involving electron localization on cerium atoms. We demonstrate that it can involve charge localization on light element impurities. © 2012 American Physical Society. Source

Jaeken B.,University of Murcia | Lundstrom L.,KTH Royal Institute of Technology | Artal P.,University of Murcia
Optics Express | Year: 2011

We designed and built a fast scanning peripheral Hartmann-Shack (HS) wave-front sensor to measure the off-axis wave-front aberrations in the human eye. The new instrument is capable of measuring the optical quality over the central 80° horizontal visual field in 1.8 seconds with an angular resolution of 1°. The subject has an open field of view without any moving elements in the line-of-sight and the head is kept in place by a head-chin rest. The same efficiency, reliability and measurement quality as the current static HS sensor were found but with much higher acquisition speed and comfort for the patients. This instrument has the potential to facilitate and improve future research on the peripheral optical quality of the eye in large groups of subjects. © 2011 Optical Society of America. Source

Ohrstrom M.,ABB | Soder L.,KTH Royal Institute of Technology
IEEE Transactions on Power Delivery | Year: 2011

In this paper, a new method is proposed that can be used to discriminate faults from switching transients. The method is primarily intended for use in systems where fast fault detection and fast fault clearing before the first peak of the fault current are required. An industrial system, in which high short-circuit power is desired but in which high short-circuit currents cannot be tolerated is an example of such a system. A phase-locked loop (PLL) is used to perform the discrimination. Computer simulations have been performed and it has been demonstrated that the output of the PLL is completely different for a fault compared to a switching transient. This difference can be used for discrimination between a fault and a switching transient. © 2011 IEEE. Source

Vallgren A.,KTH Royal Institute of Technology
Journal of Fluid Mechanics | Year: 2011

High-resolution simulations of forced two-dimensional turbulence reveal that the inverse cascade range is sensitive to an infrared Reynolds number, Re = kf/k, where kf is the forcing wavenumber and k is a frictional wavenumber based on linear friction. In the limit of high Re, the classic k5/3 scaling is lost and we obtain steeper energy spectra. The sensitivity is traced to the formation of vortices in the inverse energy cascade range. Thus, it is hypothesized that the dual limit Re and Re = kd/kf, where kd is the small-scale dissipation wavenumber, will lead to a steeper energy spectrum than k 5/3 in the inverse energy cascade range. It is also found that the inverse energy cascade is maintained by non-local triad interactions. © 2011 Cambridge University Press. Source

Levin M.,Nynas AB | Wiklund P.,Nynas AB | Leygraf C.,KTH Royal Institute of Technology
Corrosion Science | Year: 2012

The corrosion protection of copper by four bioorganic compounds; adenine, purine, cysteine and histidine, in hydrocarbon media has been examined by in situ ellipsometry, atom absorption spectroscopy and a standard corrosion test. Adenine and purine were found to irreversibly bind to the copper surface. The amount of dissolved copper was severely lowered and the copper surface appeared unaffected. It was concluded that adenine and purine exhibited a surface passivating effect, whereas the effect of cysteine and histidine was significantly lower. The influence on oxidation stability of the medium by addition of the compounds was examined and found to be minor. © 2012 Elsevier Ltd. Source

Manyuhina O.V.,KTH Royal Institute of Technology | Amar M.B.,Ecole Normale Superieure de Paris
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2013

We study theoretically the formation of long-wavelength instability patterns observed at spreading of nematic droplets on liquid substrates. The role of surface-like elastic terms in nematic films of submicron thickness is (re)examined by extending our previous work to hybrid aligned nematics. We identify the upper threshold for the formation of stripes and compare our results with experimental observations. We find that the wavelength and the amplitude of the in-plane director undulations can be related to the small but finite azimuthal anchoring. Within a simplified model we analyse the possibility of non-planar base state below the Barbero-Barberi critical thickness. © 2013 Elsevier B.V. Source

Zhang L.,ABB | Harnefors L.,ABB | Nee H.-P.,KTH Royal Institute of Technology
IEEE Transactions on Power Systems | Year: 2011

The recently proposed power-synchronization control for grid-connected voltage-source converters (VSCs) has been shown to be a feasible solution for high-voltage direct-current (HVDC) transmission connected to high-impedance weak ac systems. In this paper, power-synchronization control is investigated for VSC-HVDC links connected to another type of weak ac system, i.e., low-inertia or island systems. As an example, a linear model of a typical island system feeding by a VSC-HVDC link, including a synchronous generator, an induction motor, and some passive loads, is developed for tuning the control parameters of the VSC-HVDC link. Time simulations in PSCAD/EMTDC demonstrate that VSC-HVDC systems using power-synchronization control are flexible for various network conditions, such as large-ac-system connection, island systems, or passive networks. The time simulations also show that power-synchronization control can seamlessly handle transitions between operation modes, as well as ride through ac-system faults in all network conditions. © 2010 IEEE. Source

Ye Y.Q.,Zhejiang University | Jin Y.,Zhejiang University | He S.,Zhejiang University | He S.,KTH Royal Institute of Technology
Journal of the Optical Society of America B: Optical Physics | Year: 2010

A nearly omnidirectional THz absorber for both transverse electric (TE) and transverse magnetic (TM) polarizations is proposed. Through the excitation of the magnetic polariton in a metal-dielectric layer, the incident light is perfectly absorbed in a thin thickness that is about 25 times smaller than the resonance wavelength. By simply stacking several such structural layers with different geometrical dimensions, the bandwidth of this strong absorption can be effectively enhanced due to the hybridization of magnetic polaritons in different layers. © 2010 Optical Society of America. Source

Huang S.,KTH Royal Institute of Technology
Proceedings of the Annual ACM Symposium on Theory of Computing | Year: 2013

We prove that for all integer k ≥ 3, there is a predicate P on k Boolean variables with 2 Õ (k1/3) accepting assignments that is approximation resistant even on satisiable instances. That is, given a satisfiable CSP instance with constraint P, we cannot achieve better approximation ratio than simply picking random assignments. This improves the best previously known result by Håstad and Khot where the predicate has 2O(k1/2) accepting assignments. Our construction is inspired by several recent developments. One is the idea of using direct sums to improve soundness of PCPs, developed by Chan [5]. We also use techniques from Wenner [32] to construct PCPs with perfect completeness without relying on the d-to-1 Conjecture. Copyright 2013 ACM. Source

Liu J.-Y.,Tianjin University of Technology | Zhou S.,KTH Royal Institute of Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

Motivated by recent measurements of a relatively large θ13 in the Daya Bay and RENO reactor neutrino experiments, we carry out a systematic analysis of the hybrid textures of Majorana neutrino mass matrix Mν, which contain one texture zero and two equal nonzero matrix elements. We show that three neutrino masses (m1,m2,m 3) and three leptonic CP-violating phases (δ,ρ,σ) can fully be determined from two neutrino mass-squared differences (δm2,Δm2) and three flavor mixing angles (θ12, θ23,θ13). Out of sixty logically possible patterns of Mν, thirty-nine are found to be compatible with current experimental data at the 3σ level. We demonstrate that the texture zero of Mν is stable against one-loop quantum corrections, while the equality between two independent elements not. Phenomenological implications of Mν for the neutrinoless double-beta decay and leptonic CP violation are discussed, and a realization of the texture zero and equality by means of discrete flavor symmetries is illustrated. © 2013 American Physical Society. Source

Edge J.M.,KTH Royal Institute of Technology | Asboth J.K.,Hungarian Academy of Sciences
Physical Review B - Condensed Matter and Materials Physics | Year: 2015

We investigate time-independent disorder on several two-dimensional discrete-time quantum walks. We find numerically that, contrary to claims in the literature, random onsite phase disorder, spin-dependent or otherwise, cannot localize the Hadamard quantum walk; rather, it induces diffusive spreading of the walker. In contrast, split-step quantum walks are generically localized by phase disorder. We explain this difference by showing that the Hadamard walk is a special case of the split-step quantum walk, with parameters tuned to a critical point at a topological phase transition. We show that the topological phase transition can also be reached by introducing strong disorder in the rotation angles. We determine the critical exponent for the divergence of the localization length at the topological phase transition, and find ν=2.6, in both cases. This places the two-dimensional split-step quantum walk in the universality class of the quantum Hall effect. © 2015 American Physical Society. Source

Guan X.,Zhejiang University | Wu H.,Zhejiang University | Shi Y.,Zhejiang University | Wosinski L.,KTH Royal Institute of Technology | Dai D.,Zhejiang University
Optics Letters | Year: 2013

An ultracompact polarization beam splitter (PBS) is proposed based on an asymmetrical directional coupler consisting of a silicon hybrid plasmonic waveguide (HPW) and a silicon nanowire. The widths of the two coupling waveguides are chosen so that the phase-matching condition is satisfied for TE polarization only while the phase mismatch is significant for TM polarization. A sharply bent silicon HPW is connected at the thru port to play the role of polarizer by utilizing its polarization-dependent loss. With the present principle, the designed PBS has a footprint as small as only ∼1.9 μm × 3.7 μm, which is the shortest PBS reported until now, even when large waveguide dimensions (e.g., the waveguide widths w1;2 = ∼300 nm and the gap width wgap = ∼200 nm) are chosen to simplify the fabrication process. The numerical simulations show that the designed PBS has a very broad band (∼120 nm) with an extinction ratio >12 dB and a large fabrication tolerance to allow a waveguide width variation of ±30 nm. © 2013 Optical Society of America. Source

Sun F.,Zhejiang University | He S.,KTH Royal Institute of Technology
Progress in Electromagnetics Research | Year: 2010

Both explicit analysis and FEM numerical simulation are used to analyze the field distribution of a line current in the so-called Maxwell's fish eye lens [bounded with a perfectly electrical conductor (PEC) boundary]. We show that such a 2D Maxwell's fish eye lens cannot give perfect imaging due to the fact that high order modes of the object field can hardly reach the image point in Maxwell's fish eye lens. If only zeroth order mode is excited, a good image of a sharp object may be achieved in some cases, however, its spot-size is larger than the spot size of the initial object field. The image resolution is determined by the field spot size of the image corresponding to the zeroth order component of the object field. Our explicit analysis consists very well with the FEM results for a fish eye lens. Time-domain simulation is also given to verify our conclusion. Multi-point images for a single object point are also demonstrated. Source

HAkansson A.,KTH Royal Institute of Technology
Procedia Computer Science | Year: 2013

AI-complete systems developed today, are commonly used for solving different artificial intelligence problems. A problem is a typical image recognition or speech recognition, but it can also be language processing, as well as, other complex systems dealing with general problem solving. However, no AI-complete system, which models the human brain or behavior, can exist without looking at the totality of the whole situation and, and hence, incorporating an AI-computerized sensory systems into a totality that constitute a combination of senses. This paper proposes a combination of sensory systems to form a comprehensive AI-system by combining the different senses, called AIC-AI-system for a combination of senses. The AIC-system is not a complete system in the sense that it contains a total set of information or uses all kinds of digital sensory systems. Nonetheless, it is a system under self-development. It develops its own knowledge base, as experiences, which will be based on the different characteristics: images, sounds, smells, tastes, touches with emotions/feelings and expressions. The result is a kind of perception of the surrounding environment. © 2013 The Authors. Source

Cats O.,KTH Royal Institute of Technology
Procedia Computer Science | Year: 2013

Transit systems exercise complex dynamics and evolve through the interaction of various agents. The analysis of transit performance requires emulating the dynamic loading of travellers and their interaction with the underlying transit system. Multi-agent simulations aim to mimic the emergence of global spontaneous order from numerous inter-dependent local decisions. This paper presents a framework for a multi-agent transit operations and assignment model which captures supply uncertainties and adaptive user decisions. An iterative day-to-day learning process consisting of a within-day dynamic network loading loop simulates the interaction between transit supply and demand. The model requires the development and integration of several modules including traffic simulation, transit operations and control, dynamic path choice model and real-time information generator. BusMezzo, a transit simulation model, is used as the platform for implementation. © 2013 The Authors. Published by Elsevier B.V. Source

Zhang W.,Zhejiang University | Li Q.,Zhejiang University | Qiu M.,Zhejiang University | Qiu M.,KTH Royal Institute of Technology
Optics Express | Year: 2013

The determination of nanoscale distances or distance changes necessitates a nanoscale ruler. In the present paper, distance dependence of particle temperature in an optically heated gold nanoparticle pair is quantitatively investigated to explore the possibility of creating a Plasmon ruler based on this effect. The two origins of the distance-dependence, i.e., electromagnetic coupling and thermal accumulative effect, are studied. For the particle temperature, a scaling behavior is found, and it suggests that the decay of particle temperature with the interparticle gap for different particle sizes follows a common exponential decay equation. This scaling behavior is qualitatively explained with a simple dipolar-coupling model combined with a point heat source interaction model. On the basis of this scaling behavior of absorption power, we further establish a plasmon ruler equation relating the particle temperature and the interparticle distance. Our findings can serve as an excellent guideline for designing and optimizing temperature-based plasmon rulers. © 2013 Optical Society of America. Source

Ong Y.C.,KTH Royal Institute of Technology
General Relativity and Gravitation | Year: 2015

Classically, black holes admit maximal interior volumes that grow asymptotically linearly in time. We show that such volumes remain large when Hawking evaporation is taken into account. Even if a charged black hole approaches the extremal limit during this evolution, its volume continues to grow; although an exactly extremal black hole does not have a “large interior”. We clarify this point and discuss the implications of our results to the information loss and firewall paradoxes. © 2015, Springer Science+Business Media New York. Source

Heisenberg L.,KTH Royal Institute of Technology | Heisenberg L.,The Oskar Klein Center
Journal of Cosmology and Astroparticle Physics | Year: 2015

In the context of massive gravity, bi-gravity and multi-gravity non-minimal matter couplings via a specific composite effective metric were investigated recently. Even if these couplings generically reintroduce the Boulware-Deser ghost, this composite metric is unique in the sense that the ghost reemerges only beyond the decoupling limit and the matter quantum loop corrections do not detune the potential interactions. We consider non-minimal derivative couplings of the composite metric to matter fields for a specific subclass of Horndeski scalar-tensor interactions. We first explore these couplings in the mini-superspace and investigate in which scenario the ghost remains absent. We further study these non-minimal derivative couplings in the decoupling-limit of the theory and show that the equation of motion for the helicity-0 mode remains second order in derivatives. Finally, we discuss preliminary implications for cosmology. Source

Horowitz J.M.,University of Massachusetts Boston | Sandberg H.,KTH Royal Institute of Technology
New Journal of Physics | Year: 2014

In a thermodynamic process with measurement and feedback, the second law of thermodynamics is no longer valid. In its place, various second-law-like inequalities have been advanced that each incorporate a distinct additional term accounting for the information gathered through measurement. We quantitatively compare a number of these information measures using an analytically tractable model for the feedback cooling of a Brownian particle. We find that the information measures form a hierarchy that reveals a web of interconnections. To untangle their relationships, we address the origins of the information, arguing that each information measure represents the minimum thermodynamic cost to acquire that information through a separate, distinct measurement procedure. © 2014 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. Source

Zelenina M.,Karolinska Institutet | Zelenina M.,KTH Royal Institute of Technology
Neurochemistry International | Year: 2010

Three aquaporins are expressed in the brain. AQP4, the predominant brain water channel, is expressed in astrocyte endfeet facing brain capillaries, perisynaptic spaces, and nodes of Ranvier. It is implicated in brain edema formation and resolution. It is also believed to assist clearance of K+ released during neuronal activity. AQP1 is expressed in epithelial cells of choroid plexus and is implicated in cerebrospinal fluid formation. AQP9, which has been reported to be present in astrocytes and in subpopulations of neurons, is implicated in the brain energy metabolism. All three brain AQPs are strongly upregulated in brain tumors and in injured brain tissue.Water and solute transport via AQPs depends on concentration gradients across the membrane, but the magnitude of the transport is to a large extent determined by the single channel permeability of AQPs and by their abundance in the cell membrane. The future therapies will have to address not only the forces driving the water and solute transport (e.g. as mannitol infusion does in the treatment of brain edema), but also the regulation of AQPs, which provide the means for water entry to the brain, for water exit from the brain, and for redistribution of water and solutes within the brain compartments. This review summarizes the data concerning structure, permeability, role in the brain, short-term and long-term regulation of the three AQPs. © 2010 Elsevier Ltd. Source

Laguna O.H.,University of Seville | Centeno M.A.,University of Seville | Boutonnet M.,KTH Royal Institute of Technology | Odriozola J.A.,University of Seville
Applied Catalysis B: Environmental | Year: 2011

A series of Ce-Fe mixed oxides as well as the pure oxides were synthesized by the microemulsions method. The solid solution formation was established for all the Fe-doped systems and only a hardly noticeable segregation of α-Fe2O3 was appreciated for the solid with the maximum iron content (50at.% Fe). The oxygen exchange is improved for all the Fe-doped systems; however the 10at.% Fe appears as the optimal iron content for achieving the maximum oxygen vacancies concentration and the higher reducibility efficiency. The CO oxidation (TOX, PROX) is especially achieved for the solids with the lower iron contents but with a superior oxygen vacancies proportion. These Ce-Fe systems prepared from microemulsions are very attractive to be considered as supports for depositing active phases capable of enhancing oxygen exchange ability of the whole system, allowing higher CO oxidation abilities. © 2011 Elsevier B.V. Source

Edin Grimheden M.,KTH Royal Institute of Technology
Mechatronics | Year: 2013

This paper presents a study of the integration of agile methods into mechatronics design education, as performed at KTH Royal Institute of Technology. The chosen method, Scrum, and the context of the studied capstone course are presented. With the integration of Scrum into the capstone projects, an educational favorable alternative is identified, to previously used design methodologies such as more traditional stage-gate methods as the Waterfall or method or the V-model. This is due to the emphasis on early prototyping, quick feedback and incremental development. It still might not be the favorable method for use in large scale industrial development projects where formal procedures might still be preferred, but the pedagogical advantages in mechatronics education are valuable. Incremental development and rapid prototyping for example gives many opportunities for students to reflect and improve. The Scrum focus on self-organizing teams also provides a platform to practice project organization, by empowering students to take responsibility for the product development process. Among the results of this study, it is shown that it is possible and favorable to integrate Scrum in a mechatronics capstone course and that this can enhance student preparation for a future career as mechatronics designers or product developers. It is also shown that this prepares the students with a larger flexibility to handle the increased complexity in mechatronics product development and thereby enabling the project teams to deliver results faster, more reliable and with higher quality. © 2013 Elsevier Ltd. All rights reserved. Source

Jennings B.,Waterford Institute of Technology | Stadler R.,KTH Royal Institute of Technology
Journal of Network and Systems Management | Year: 2015

Resource management in a cloud environment is a hard problem, due to: the scale of modern data centers; the heterogeneity of resource types and their interdependencies; the variability and unpredictability of the load; as well as the range of objectives of the different actors in a cloud ecosystem. Consequently, both academia and industry began significant research efforts in this area. In this paper, we survey the recent literature, covering 250+ publications, and highlighting key results. We outline a conceptual framework for cloud resource management and use it to structure the state-of-the-art review. Based on our analysis, we identify five challenges for future investigation. These relate to: providing predictable performance for cloud-hosted applications; achieving global manageability for cloud systems; engineering scalable resource management systems; understanding economic behavior and cloud pricing; and developing solutions for the mobile cloud paradigm. © 2014, Springer Science+Business Media New York. Source

Jebari K.,KTH Royal Institute of Technology
Science and Engineering Ethics | Year: 2015

A small but growing number of studies have aimed to understand, assess and reduce existential risks, or risks that threaten the continued existence of mankind. However, most attention has been focused on known and tangible risks. This paper proposes a heuristic for reducing the risk of black swan extinction events. These events are, as the name suggests, stochastic and unforeseen when they happen. Decision theory based on a fixed model of possible outcomes cannot properly deal with this kind of event. Neither can probabilistic risk analysis. This paper will argue that the approach that is referred to as engineering safety could be applied to reducing the risk from black swan extinction events. It will also propose a conceptual sketch of how such a strategy may be implemented: isolated, self-sufficient, and continuously manned underground refuges. Some characteristics of such refuges are also described, in particular the psychosocial aspects. Furthermore, it is argued that this implementation of the engineering safety strategy safety barriers would be effective and plausible and could reduce the risk of an extinction event in a wide range of possible (known and unknown) scenarios. Considering the staggering opportunity cost of an existential catastrophe, such strategies ought to be explored more vigorously. © 2014, Springer Science+Business Media Dordrecht. Source

Dilner D.,KTH Royal Institute of Technology
Calphad: Computer Coupling of Phase Diagrams and Thermochemistry | Year: 2016

A thermodynamic description of the Fe-Mn-Ca-Mg-S system is presented. The compound energy formalism is used to describe all solution phases. This work includes assessments of all quaternary systems as well as the ternary systems Ca-Mg-S, Ca-Mn-S and Mg-Mn-S and the binary Ca-Mn system. The remaining ternary sulphur systems and lower-order systems were taken from previous assessments. The description of the solid phases reproduces the available experimental information well. However, due to lack of experimental data, approximations are used for the liquid in the Ca-Mg-S and Mg-Mn-S systems. The thermodynamic description presented in this work can be used to perform calculations related to sulphides in steels. © 2016 Elsevier Ltd. All rights reserved. Source

Duguet Y.,CNRS Computer Science Laboratory for Mechanics and Engineering Sciences | Schlatter P.,KTH Royal Institute of Technology
Physical Review Letters | Year: 2013

Localized structures such as turbulent stripes and turbulent spots are typical features of transitional wall-bounded flows in the subcritical regime. Based on an assumption for scale separation between large and small scales, we show analytically that the corresponding laminar-turbulent interfaces are always oblique with respect to the mean direction of the flow. In the case of plane Couette flow, the mismatch between the streamwise flow rates near the boundaries of the turbulence patch generates a large-scale flow with a nonzero spanwise component. Advection of the small-scale turbulent fluctuations (streaks) by the corresponding large-scale flow distorts the shape of the turbulence patch and is responsible for its oblique growth. This mechanism can be easily extended to other subcritical flows such as plane Poiseuille flow or Taylor-Couette flow. © 2013 American Physical Society. Source

Hakkarainen M.,KTH Royal Institute of Technology
Advances in Polymer Science | Year: 2012

The stability and durability of polymeric materials under different external influences (e.g., sunlight, humidity, heat, chemicals, or microorganisms) is of outmost importance in applications such as coatings, building materials, and automotive parts, whereas a rapidly degradable material is preferable in temporary short-term applications. There are considerable economic and environmental benefits if we can design polymers for short or long lifetimes as well as prevent the release of harmful substances from the materials during their lifetime. The recent developments in mass spectrometric techniques facilitate possibilities for molecular level characterization of the changes taking place in the polymer matrix as well as for identification of the released degradation products. This review presents an overview of the application of electrospray ionization-mass spectrometry (ESI-MS) for the analysis of polymer degradation. The great potential of the technique for revealing detailed insights into the degradative reactions taking place is demonstrated with examples ranging from degradable polymers and biomaterials to degradation of coatings, paints, polymer electrolyte membranes, food packaging, and materials in the nuclear industry. © 2011 Springer-Verlag Berlin Heidelberg. Source

In the present study, differential scanning calorimetry was employed to investigate the temperature induced phase separation process of poly(propylene oxide) in a pure aqueous solution and in the presence of five different potassium salts at three different concentrations. The different salts affected the phase separation temperature in accordance with the Hofmeister series with the three salts, KF, KCl and KBr, inducing a clear salting-out effect, one salt, KSCN, inducing a clear salting-in effect and one borderline salt, KI, showing a salting-in or a salting-out effect depending on the salt concentration. It was further observed that the phase separation enthalpy was almost unaffected by the presence of KF, KCl, KBr and KI, while the presence of KSCN led to a significant decrease in this quantity. This suggests that KF, KCl, KBr and KI have a very moderate influence on the PPO hydration, while KSCN appears to decrease the hydrophobic hydration of the PPO chains. The order of how the salts affect the phase separation temperature is in agreement with data for the partition coefficients of the anions between bulk water and at the air-water interface, but only partially in agreement with data related to ion hydration and water structuring effects. These observations are discussed in relation to existing models of how the different nature of the ion and polymer hydration can lead to effective attractive and repulsive ion-polymer interactions depending of the exact chemistry of the ions and the polymer. It is suggested that the previous confusion about the Hofmeister effect is due to a misleading conceptual picture of how polymer hydration is affected by the presence of ions. It is concluded that the Hofmeister effects, in the present case, can be described by a balance between the effective interactions governed by the asymmetric hydration of ions and hydrophobic polymers. This journal is © 2012 The Royal Society of Chemistry. Source

Zalejska-Jonsson A.,KTH Royal Institute of Technology
Building and Environment | Year: 2012

The aim of this paper is to investigate building performance from the occupants' perspective and to compare how the residents in low-energy multi-family buildings and conventional buildings, respectively, perceive the comfort of, and satisfaction with, indoor elements. Additionally, the study explores differences in living-in, operation and management in low-energy and conventional residential buildings. The key data was obtained by surveys sent to occupants of carefully selected comparable buildings: three low-energy and three conventional residential buildings. Responses were compared and statistical difference was tested by the Mann-Whitney test and the Kruskal-Wallis test. Findings indicate that both low-energy and conventional residential buildings have satisfied and less satisfied tenants. The occupants' satisfaction might decrease if thermal discomfort leads them to use supplementary heating; however, use of supplementary cooling does not have the same significance. Problems and concerns regarding ventilation and heating appeared in both types of buildings. Results suggest that, compared with conventional buildings, low-energy residential buildings required the same or less system adjustment, which suggests that, from a lifecycle perspective, the low-energy buildings are the better investment. Occupants' responses suggest that the " green" profile of the building has a positive impact on their environmental awareness and behaviour. This paper shows that occupants' feedback is an important part of comprehensive building performance assessment, indicating areas for improvement relevant for developers and housing managers. The presented results show that problems often identified as specific to low-energy buildings also appear in conventional buildings. © 2012 Elsevier Ltd. Source

Karrbom Gustavsson T.,KTH Royal Institute of Technology
International Journal of Project Management | Year: 2016

While project work can be motivating, stimulating and creative, it can also be frustrating, ambiguous and stressful. Situations of project overload, i.e. situations in which fragmentation, disturbances and disruptions are reoccurring, are common in project-based organizations running many parallel projects. This paper reports findings from an extensive interview study on how project managers and project members working in parallel projects handle project overload by changing their work routines. The results show 1) that project work in practice is organized by using narrowing strategies and 2) that narrowing strategies run the risk of excluding the vital historical and organizational context. The findings have implications for project theory and project practice. © 2015 Elsevier Ltd and Association for Project Management and the International Project Management Association. Source

Fischione C.,KTH Royal Institute of Technology
IEEE Transactions on Automatic Control | Year: 2011

Motivated by the need for fast computations in wireless sensor networks, the new F-Lipschitz optimization theory is introduced for a novel class of optimization problems. These problems are defined by simple qualifying properties specified in terms of increasing objective function and contractive constraints. It is shown that feasible F-Lipschitz problems have always a unique optimal solution that satisfies the constraints at equality. The solution is obtained quickly by asynchronous algorithms of certified convergence. F-Lipschitz optimization can be applied to both centralized and distributed optimization. Compared to traditional Lagrangian methods, which often converge linearly, the convergence time of centralized F-Lipschitz problems is at least superlinear. Distributed F-Lipschitz algorithms converge fast, as opposed to traditional Lagrangian decomposition and parallelization methods, which generally converge slowly and at the price of many message passings. In both cases, the computational complexity is much lower than traditional Lagrangian methods. Examples of application of the new optimization method are given for distributed estimation and radio power control in wireless sensor networks. The drawback of the F-Lipschitz optimization is that it might be difficult to check the qualifying properties. For more general optimization problems, it is suggested that it is convenient to have conditions ensuring that the solution satisfies the constraints at equality. © 2011 IEEE. Source

Blom H.,KTH Royal Institute of Technology | Widengren J.,Albanova University Center
Current Opinion in Chemical Biology | Year: 2014

High resolution Stimulated Emission Depletion (STED) microscopy has been demonstrated for fundamental studies in cells, living tissue and organisms. Today, a major trend in the STED technique development is to make the instruments simpler and more user-friendly, without compromising performance. This has become possible by new low-cost, turn-key laser technology and by implementing specifically designed phase plates and polarization elements, extending and simplifying the shaping of the laser beam profiles. These simpler and cheaper realizations of STED are now becoming more broadly available. In parallel with the continuous development of sample preparation and fluorophore reporter molecules ultimately setting the limit of the image quality, contrast and resolution, we can thus expect a significant increase in the use of STED, in science as well as for clinical and drug development purposes. © 2014. Source

This study analysed the environmental follow-up of a public organisation from a systems thinking approach, including follow-up within different phases of operation and with different environmental management tools. The Swedish Rail Administration (SRA), a public authority responsible for Swedish rail infrastructure, was used as a case organisation. The main aim was to identify different follow-up activities during planning, construction and operation of rail infrastructure. Additional aims were to identify limiting factors for effective environmental follow-up and to provide suggestions on how SRA follow-up can better be used as an organisational learning tool. The follow-up proved to be highly influenced by Environmental Management System and was mainly used for showing compliance with legal regulations or contract requirements. Use of environmental monitoring data was limited to the specific project in which the follow-up was carried out, possibly because of the project-based structure of the organisation following rail deregulation. Theory on organisational learning was applied in the study to discuss how to improve the distribution and use of follow-up data. A more complete 'organisational memory' seems to be required for learning from experience and adapting to change. © 2011 Springer Science+Business Media, LLC. Source

Solomon A.R.,University of Cambridge | Akrami Y.,University of Oslo | Koivisto T.S.,KTH Royal Institute of Technology
Journal of Cosmology and Astroparticle Physics | Year: 2014

The ghost-free theory of massive gravity with two dynamical metrics has been shown to produce viable cosmological expansion, where the late-time acceleration of the Universe is due to the finite range of the gravitational interaction rather than a nonzero cosmological constant. Here the cosmological perturbations are studied in this theory. The full perturbation equations are presented in a general gauge and analyzed, focusing on subhorizon scales in the quasistatic limit during the matter-dominated era. An evolution equation for the matter inhomogeneities and the parameters quantifying the deviations from general relativistic structure formation are expressed in terms of five functions whose forms are determined directly by the coupling parameters in the theory. The evolution equation has a similar structure to Horndeski-type scalar-tensor theories, exhibiting a modified growth rate and scale-dependence at intermediate wavenumbers. Predictions of the theory are confronted with observational data on both background expansion and large-scale structure, although care must be taken to ensure a model is stable. It is found that while the stable models fit the data well, they feature deviations from the standard cosmology that could be detected or ruled out by near-future experiments. © 2014 IOP Publishing Ltd and Sissa Medialab srl . Source

Scragg J.J.,Uppsala University | Kubart T.,Uppsala University | Watjen J.T.,Uppsala University | Ericson T.,Uppsala University | And 2 more authors.
Chemistry of Materials | Year: 2013

Cu2ZnSnS4 (CZTS) is a promising material for thin film solar cells based on sustainable resources. This paper explores some consequences of the chemical instability between CZTS and the standard Mo "back contact" layer used in the solar cell. Chemical passivation of the back contact interface using titanium nitride (TiN) diffusion barriers, combined with variations in the CZTS annealing process, enables us to isolate the effects of back contact chemistry on the electrical properties of the CZTS layer that result from the synthesis, as determined by measurements on completed solar cells. It is found that instability in the back contact is responsible for large current losses in the finished solar cell, which can be distinguished from other losses that arise from instabilities in the surface of the CZTS layer during annealing. The TiN-passivated back contact is an effective barrier to sulfur atoms and therefore prevents reactions between CZTS and Mo. However, it also results in a high series resistance and thus a reduced fill factor in the solar cell. The need for high chalcogen pressure during CZTS annealing can be linked to suppression of the back contact reactions and could potentially be avoided if better inert back contacts were to be developed. © 2013 American Chemical Society. Source

The connection-set algebra (CSA) is a novel and general formalism for the description of connectivity in neuronal network models, from small-scale to large-scale structure. The algebra provides operators to form more complex sets of connections from simpler ones and also provides parameterization of such sets. CSA is expressive enough to describe a wide range of connection patterns, including multiple types of random and/or geometrically dependent connectivity, and can serve as a concise notation for network structure in scientific writing. CSA implementations allow for scalable and efficient representation of connectivity in parallel neuronal network simulators and could even allow for avoiding explicit representation of connections in computer memory. The expressiveness of CSA makes prototyping of network structure easy. A C++ version of the algebra has been implemented and used in a large-scale neuronal network simulation (Djurfeldt et al., IBM J Res Dev 52(1/2):31-42, 2008b) and an implementation in Python has been publicly released. © Springer Science+Business Media, LLC 2012. Source

McInnes B.,KTH Royal Institute of Technology | McInnes B.,National University of Singapore
Classical and Quantum Gravity | Year: 2014

Future facilities such as FAIR and NICA are expected to produce collisions of heavy ions generating quark-gluon plasmas (QGPs) with large values of the quark chemical potential; peripheral collisions in such experiments will also lead to large values of the angular momentum density, associated with the internal shearing motion of the plasma. It is well known that shearing motions in fluids can lead to instabilities which cause a transition from laminar to turbulent flow, and such instabilities in the QGP have recently attracted some attention. We set up a holographic model of this situation by constructing a gravitational dual system exhibiting an instability which is indeed triggered by shearing angular momentum in the bulk. We show that holography indicates that the transition to an unstable fluid happens more quickly as one scans across the quark matter phase diagram towards large values of the chemical potential. This may have negative consequences for the observability of quark polarization effects. © 2014 IOP Publishing Ltd. Source

Delvenne J.-C.,Catholic University of Louvain | Sandberg H.,KTH Royal Institute of Technology
Physica D: Nonlinear Phenomena | Year: 2014

In this paper, we identify a class of time-varying port-Hamiltonian systems that is suitable for studying problems at the intersection of statistical mechanics and control of physical systems. Those port-Hamiltonian systems are able to modify their internal structure as well as their interconnection with the environment over time. The framework allows us to prove the First and Second Laws of thermodynamics, but also lets us apply results from optimal and stochastic control theory to physical systems. In particular, we show how to use linear control theory to optimally extract work from a single heat source over a finite time interval in the manner of Maxwell's demon. Furthermore, the optimal controller is a time-varying port-Hamiltonian system, which can be physically implemented as a variable linear capacitor and transformer. We also use the theory to design a heat engine operating between two heat sources in finite-time Carnot-like cycles of maximum power, and we compare those two heat engines. © 2013 Elsevier Inc. All rights reserved. Source

Hansson S.O.,KTH Royal Institute of Technology
Artificial Intelligence | Year: 2016

According to the co-occurrence test, q is (non-monotonically) inferrible from p if and only if q holds in all the reasonably plausible belief change outcomes in which p holds. A formal model is introduced that contains representations of both the co-occurrence test (for non-monotonic inference) and the Ramsey test (for conditionals). In this model, (non-nested) conditionals and non-monotonic inference satisfy the same logical principles. However, in spite of this similarity the two notions do not coincide. They should be carefully distinguished from each other. © 2016 Elsevier B.V. All rights reserved. Source

Kasson P.M.,University of Virginia | Lindahl E.,KTH Royal Institute of Technology | Lindahl E.,University of Stockholm | Pande V.S.,Stanford University
Journal of the American Chemical Society | Year: 2011

Membrane interfaces are critical to many cellular functions, yet the vast array of molecular components involved make the fundamental physics of interaction difficult to define. Water has been shown to play an important role in the dynamics of small biological systems, for example when trapped in hydrophobic regions, but the molecular details of water have generally been thought dispensable when considering large membrane interfaces. Nevertheless, spectroscopic data indicate that water has distinct, ordered behavior near membrane surfaces. While coarse-grained simulations have achieved success recently in aiding understanding the dynamics of membrane assemblies, it is natural to ask, does the missing chemical nature of water play an important role? We have therefore performed atomic-resolution simulations of vesicle fusion to understand the role of chemical detail, particularly the molecular structure of water, in membrane fusion and at membrane interfaces more generally. These membrane interfaces present a form of hydrophilic confinement, yielding surprising, non-bulk-like water behavior. © 2011 American Chemical Society. Source

Qi C.,KTH Royal Institute of Technology
Reviews in Physics | Year: 2016

The advent of radioactive ion beam facilities and new detector technologies have opened up new possibilities to investigate the radioactive decays of highly unstable nuclei, in particular the proton emission, α decay and heavy cluster decays from neutron-deficient (or proton-rich) nuclei around the proton drip line. It turns out that these decay measurements can serve as a unique probe for studying the structure of the nuclei involved. On the theoretical side, the development in nuclear many-body theories and supercomputing facilities have also made it possible to simulate the nuclear clusterization and decays from a microscopic and consistent perspective. In this article we would like to review the current status of these structure and decay studies in heavy nuclei, regarding both experimental and theoretical opportunities. We then discuss in detail the recent progress in our understanding of the nuclear α formation probabilities in heavy nuclei and their indication on the underlying nuclear structure. © 2016 The Authors. Source

Gorton D.,KTH Royal Institute of Technology
Risk Analysis | Year: 2014

The article introduces the use of probabilistic risk assessment for modeling the incident response process of online financial services. The main contribution is the creation of incident response trees, using event tree analysis, which provides us with a visual tool and a systematic way to estimate the probability of a successful incident response process against the currently known risk landscape, making it possible to measure the balance between front-end and back-end security measures. The model is presented using an illustrative example, and is then applied to the incident response process of a Swedish bank. Access to relevant data is verified and the applicability and usability of the proposed model is verified using one year of historical data. Potential advantages and possible shortcomings are discussed, referring to both the design phase and the operational phase, and future work is presented. © 2014 Society for Risk Analysis. Source

Liu X.-W.,Hefei University of Technology | Zhou S.,KTH Royal Institute of Technology
International Journal of Modern Physics A | Year: 2013

The Daya Bay and RENO reactor neutrino experiments have revealed that the smallest neutrino mixing angle is in fact relatively large, i.e. θ13 ≈9°. Motivated by this exciting progress, we perform a systematic study of the neutrino mass matrix Mν with one or two texture zeros, in the assumption that neutrinos are Dirac particles. Among 15 possible patterns with two texture zeros, only three turn out to be favored by current neutrino oscillation data at the 3σ level. Although all the six patterns with one texture zero are compatible with the experimental data at the 3σ level, the parameter space of each pattern is strictly constrained. Phenomenological implications of Mν on the leptonic CP violation and neutrino mass spectrum are explored, and the stability of texture zeros against the radiative corrections is also discussed. © 2013 World Scientific Publishing Company. Source

Fernaeus Y.,KTH Royal Institute of Technology | Sundstrom P.,University of Salzburg
Proceedings of the Designing Interactive Systems Conference, DIS '12 | Year: 2012

The topic of Materials has recently surfaced as a major theme within the research field of interaction design. In this paper we further discuss the need for in-depth descriptions of specific design cases, by revisiting some of our own research-through-design efforts when working with new or not yet fully explored materials for mobile interaction. We outline a series of design challenges that we see commonly arising in this domain, divided into three general themes; 1) affordances of hardware and casings, 2) experiential properties of different software solution, and 3) material properties of sensors, radio-signals, and electricity. Our main conclusion is that research in interaction design needs an extended focus on how systems are crafted from and together with properties of digital materials, and how new knowledge gained from those processes can be shared. © 2012 ACM. Source

Lowe D.A.,Brown University | Thorlacius L.,KTH Royal Institute of Technology | Thorlacius L.,University of Iceland
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2014

Within the framework of black hole complementarity, a proposal is made for an approximate interior effective field theory description. For generic correlators of local operators on generic black hole states, it agrees with the exact exterior description in a region of overlapping validity, up to corrections that are too small to be measured by typical infalling observers. © 2014 The Authors. Source

Jimenez J.B.,Leuven University | Koivisto T.S.,University of Oslo | Koivisto T.S.,KTH Royal Institute of Technology
Classical and Quantum Gravity | Year: 2014

In this paper we consider an extended Gauss-Bonnet gravity theory in arbitrary dimensions and in a space provided with a Weyl connection, which is torsion-free but non-metric-compatible, the non-metricity tensor being determined by a vector field. The action considered consists of the usual Einstein-Hilbert action plus all the terms quadratic in the curvature that reduce to the usual Gauss-Bonnet term for vanishing Weyl connection, i.e., when only the Levi-Civita part of the connection is present. We expand the action in terms of Riemannian quantities and obtain vector-tensor theories. We find that all the free parameters only appear in the kinetic term of the vector field, so two branches are possible: one with a propagating vector field and another one where the vector field does not propagate. We focus on the propagating case. We find that in four dimensions, the theory is equivalent to Einstein's gravity plus a Proca field. This field is naturally decoupled from matter, so it represents a natural dark matter candidate. Also for d = 4, we discuss a non-trivial cubic term in the curvature that can be constructed without spoiling the second-order nature of the field equations, because it leads to the vector-tensor Horndeski interaction. In arbitrary dimensions, the theory becomes more involved. We show that, even though the vector field presents kinetic interactions which do not have symmetry, there are no additional propagating degrees of freedom with respect to the usual massive case. We show that, interestingly, this relies on the fact that the corresponding Stückelberg field belongs to a specific class within the general Horndeski theories. Finally, since Weyl geometries provide the natural ground on which to build scale invariant theories, we apply the usual Weyl gauging in order to make the Horndeski action locally scale invariant, and discuss new terms that can be added. © 2014 IOP Publishing Ltd. Source

Ruban A.V.,KTH Royal Institute of Technology
Philosophical Magazine | Year: 2014

A single-site mean-field approach for the concentration of thermal defects in a binary intermetallic AB compound is proposed, which is a modification of previously existing Wagner-Schottky-type models. A numerical investigation of the model is done for the case of thermal defects in NiAl. © 2014 Taylor and Francis. Source

Feng L.,KTH Royal Institute of Technology | Wonham W.M.,University of Toronto
Discrete Event Dynamic Systems: Theory and Applications | Year: 2010

Natural projections with the observer property have proved effective in reducing the computational complexity of nonblocking supervisory control design, and the state sizes of the resulting controllers. In this paper we present an algorithm to verify this property, or if necessary to achieve it. A natural projection is a special type of general causal reporter map; for the latter an algorithm is already known for verification and modification. This algorithm could be used to verify the observer property of a natural projection, but if the natural projection is not an observer the algorithm is not applicable to modify it to an observer. Also, while a general reporter map always admits a unique smallest refinement with the observer property, a natural projection does not. Indeed there may exist several minimal extensions to the original observable event set of a natural projection. We show that the problem of finding a minimal extension is NP-hard, but propose a polynomial-time algorithm that always finds an acceptable extension. While not guaranteed to be minimal, it is in practice often reasonably small. © 2008 Springer Science+Business Media, LLC. Source

Jarall S.,KTH Royal Institute of Technology
International Journal of Refrigeration | Year: 2012

Theoretical cycle data and heat transfer of HFO-1234yf were calculated and compared with those of R134a. Drop-in tests for R134a and HFO-1234yf were carried out using refrigeration unit of a hermetic rotary compressor of 550 W nominal output power and plate heat exchangers. Results of the evaporator cooling effect and heat transfer, COP, and compressor efficiency at a defined condensation temperature and similar evaporation temperatures for the two refrigerants were calculated and compared. © 2012 Elsevier Ltd and IIR. All rights reserved. Source

Federico S.,University of Calgary | Gasser T.C.,KTH Royal Institute of Technology
Journal of the Royal Society Interface | Year: 2010

The elastic strain energy potential for nonlinear fibre-reinforced materials is customarily obtained by superposition of the potentials of the matrix and of each family of fibres. Composites with statistically oriented fibres, such as biological tissues, can be seen as being reinforced by a continuous infinity of fibre families, the orientation of which can be represented by means of a probability density function defined on the unit sphere (i.e. the solid angle). In this case, the superposition procedure gives rise to an integral form of the elastic potential such that the deformation features in the integral, which therefore cannot be calculated a priori. As a consequence, an analytical use of this potential is impossible. In this paper, we implemented this integral form of the elastic potential into a numerical procedure that evaluates the potential, the stress and the elasticity tensor at each deformation step. The numerical integration over the unit sphere is performed by means of the method of spherical designs, in which the result of the integral is approximated by a suitable sum over a discrete subset of the unit sphere. As an example of application, we modelled the collagen fibre distribution in articular cartilage, and used it in simulating displacement-controlled tests: the unconfined compression of a cylindrical sample and the contact problem in the hip joint. © 2010 The Royal Society. Source

Flotterod G.,KTH Royal Institute of Technology | Liu R.,University of Leeds
Journal of Intelligent Transportation Systems: Technology, Planning, and Operations | Year: 2014

This article describes the first application of a novel path flow and origin/destination (OD) matrix estimator for iterated dynamic traffic assignment (DTA) microsimulations. The presented approach, which operates on a trip-based demand representation, is derived from an agent-based DTA calibration methodology that relies on an activity-based demand model (Flötteröd, Bierlaire, & Nagel, 2011). The objective of this work is to demonstrate the transferability of the agent-based approach to the more widely used OD matrix-based demand representation. The calibration (i) operates at the same disaggregate level as the microsimulation and (ii) has drastic computational advantages over conventional OD matrix estimators in that the demand adjustments are conducted within the iterative loop of the DTA microsimulation, which results in a running time of the calibration that is in the same order of magnitude as a plain simulation. We describe an application of this methodology to the trip-based DRACULA microsimulation and present an illustrative example that clarifies its capabilities. © 2014 Copyright © Taylor and Francis Group, LLC. Source

Guo F.,U.S. National Institute of Standards and Technology | Guo F.,University of Maryland University College | Belova L.M.,University of Maryland University College | McMichael R.D.,KTH Royal Institute of Technology
Physical Review Letters | Year: 2013

We report ferromagnetic resonance force microscopy of confined spin-wave modes with improved, 100 nm resolution. The ferromagnetic resonance spectra in Permalloy disks (diameters ranging from 100 to 750 nm) distinguish multiple edge modes, and the images reveal distinct precession patterns. The fundamental edge mode also provides a new, localized probe of the magnetic properties of the film edge; rotation of the applied field reveals large edge property variations in nominally circular disks. As a function of disk diameter, the number of observed edge modes agrees with modeling. © 2013 American Physical Society. Source

Hagfeldt A.,Uppsala University | Hagfeldt A.,KTH Royal Institute of Technology
Ambio | Year: 2012

Dye-sensitized solar cells (DSC) are based on molecular and nanometer-scale components. Record cell efficiencies of 12%, promising stability data and means of energy-efficient production methods have been accomplished. As selling points for the DSC technology the prospect of low-cost investments and fabrication are key features. DSCs offer the possibilities to design solar cells with a large flexibility in shape, color, and transparency. The basic principles of the operation of DSC, the state-of-the-art as well as the potentials for future development are described. © Royal Swedish Academy of Sciences 2012. Source

Chua K.J.,National University of Singapore | Chou S.K.,National University of Singapore | Yang W.M.,National University of Singapore | Yan J.,KTH Royal Institute of Technology | Yan J.,Malardalen University
Applied Energy | Year: 2013

Air conditioning is essential for maintaining thermal comfort in indoor environments, particularly for hot and humid climates. Today, air conditioning, comprising cooling and dehumidification, has become a necessity in commercial and residential buildings and industrial processes. It accounts for a major share of the energy consumption of a building or facility. In tropical climates, the energy consumed by heating, ventilation and air-conditioning (HVAC) can exceed 50% of the total energy consumption of a building. This significant figure is primarily due to the heavy duty placed on cooling technologies to remove both sensible and latent heat loads. Therefore, there is tremendous potential to improve the overall efficiency of the air-conditioning systems in buildings.Based on today's practical technology for cooling, the major components of a chiller plant are (1) compressors, (2) cooling towers, (3) pumps (chilled and cooling water) and (4) fans in air handling units. They all consume mainly electricity to operate. When specifying the kW/R. ton of a plant, there are two levels of monitoring cooling efficiency: (1) at the efficiency of the chiller machines or the compressors which consume a major amount of electricity; and (2) at the overall efficiency of cooling plants which include the cooling towers, pumps for moving coolant (chilled and cooling water) to all air-handling units. Pragmatically, a holistic approach is necessary towards achieving a low energy input per cooling achieved such as 0.6. kW/R. ton cooling or lower by considering all aspects of the cooling plant.In this paper, we present a review of recent innovative cooling technology and strategies that could potentially lower the kW/R. ton of cooling systems - from the existing mean of 0.9. kW/R. ton towards 0.6. kW/R. ton or lower. The paper, broadly divided into three key sections (see Fig. 2), begins with a review of the recent novel devices that enhances the energy efficiency of cooling systems at the component level. This is followed by a review of innovative cooling systems designs that reduces energy use for air conditioning. Lastly, the paper presents recent developments in intelligent air-control strategies and smart chiller sequencing methodologies that reduce the primary energy utilization for cooling.The energy efficient cooling technology, innovative systems designs, and intelligent control strategies described in the paper have been recently researched or are on-going studies. Several have been implemented on a larger scale and, therefore, are examples of practical solutions that can be readily applied to suit specific needs. © 2012 Elsevier Ltd. Source

Janmark J.,KTH Royal Institute of Technology | Janmark J.,University of California at San Diego | Meyer D.A.,University of California at San Diego | Wong T.G.,University of California at San Diego
Physical Review Letters | Year: 2014

Grover's quantum search algorithm can be formulated as a quantum particle randomly walking on the (highly symmetric) complete graph, with one vertex marked by a nonzero potential. From an initial equal superposition, the state evolves in a two-dimensional subspace. Strongly regular graphs have a local symmetry that ensures that the state evolves in a three-dimensional subspace but most have no global symmetry. Using degenerate perturbation theory, we show that quantum random walk search on known families of strongly regular graphs, nevertheless, achieves the full quantum speed-up of Θ(N), disproving the intuition that fast quantum search requires global symmetry. © 2014 American Physical Society. Source

Parmryd I.,Uppsala University | Onfelt B.,KTH Royal Institute of Technology | Onfelt B.,Karolinska Institutet
FEBS Journal | Year: 2013

The surface of mammalian cells is neither smooth nor flat and cells have several times more plasma membrane than the minimum area required to accommodate their shape. We discuss the biological function of this apparent excess membrane that allows the cells to migrate and undergo shape changes and probably plays a role in signal transduction. Methods for studying membrane folding and topography - atomic force microscopy, scanning ion conductance microscopy, fluorescence polarization microscopy and linear dichroism - are described and evaluated. Membrane folding and topography is frequently ignored when interpreting microscopy data. This has resulted in several misconceptions regarding for instance colocalization, membrane organization and molecular clustering. We suggest simple ways to avoid these pitfalls and invoke Occam's razor - that simple explanations are preferable to complex ones. Topography, i.e. deviations from a smooth surface, should always be ruled out as the cause of anomalous data before other explanations are presented. Cell membranes are convoluted into submicrometer ruffles, which are impossible to resolve by most experimental techniques. Here we discuss the importance of considering such subresolution membrane organization when interpreting experimental data and give some examples of techniques where membrane topography can be probed. Finally we speculate what consequences ruffling could have for cellular processes, e. g. receptor signaling. © 2013 The Authors Journal compilation © 2013 FEBS. Source

Larjo K.,Brown University | Lowe D.A.,Brown University | Thorlacius L.,KTH Royal Institute of Technology | Thorlacius L.,University of Iceland
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

The postulates of black hole complementarity do not imply a firewall for infalling observers at a black hole horizon. The dynamics of the stretched horizon, that scrambles and reemits information, determines whether infalling observers experience anything out of the ordinary when entering a large black hole. In particular, there is no firewall if the stretched horizon degrees of freedom retain information for a time of the order of the black hole scrambling time. © 2013 American Physical Society. Source

Hansson S.O.,KTH Royal Institute of Technology
Science and Engineering Ethics | Year: 2011

Research is subject to more stringent ethical requirements than most other human activities, and a procedure that is otherwise allowed may be forbidden in research. Hence, risk-taking is more restricted in scientific research than in most non-research contexts, and privacy is better protected in scientific questionnaires than in marketing surveys. Potential arguments for this difference are scrutinized. The case in its favour appears to be weak. A stronger case can be made in favour of a difference in the opposite direction: If perilous or otherwise problematic activities have to be performed it is usually better to perform them in a research context where they are properly evaluated so that guidance is obtained for the future. However, retreating from current ethical demands on research is not a desirable direction to go. Instead, research ethics can serve to inspire the introduction of more stringent ethical principles in other social sectors. © 2009 Springer Science+Business Media B.V. Source

Gouteraux B.,KTH Royal Institute of Technology
Journal of High Energy Physics | Year: 2014

We show that strongly-coupled, translation-invariant holographic IR phases at finite density can be classified according to the scaling behaviour of the metric, the electric potential and the electric flux introducing four critical exponents, independently of the details of the setup. Solutions fall into two classes, depending on whether they break relativistic symmetry or not. The critical exponents determine key properties of these phases, like thermodynamic stability, the (ir)relevant deformations around them, the low-frequency scaling of the optical conductivity and the nature of the spectrum for electric perturbations. We also study the scaling behaviour of the electric flux through bulk minimal surfaces using the Hartnoll-Radicevic order parameter, and characterize the deviation from the Ryu-Takayanagi prescription in terms of the criti cal exponents. © 2014 The Author(s). Source

Hossenfelder S.,KTH Royal Institute of Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

If space-time is emergent from a fundamentally nongeometric theory it will generically be left with defects. Such defects need not respect the locality that emerges with the background. Here, we develop a phenomenological model that parametrizes the effects of nonlocal defects on the propagation of particles. In this model, Lorentz invariance is preserved on the average. We derive constraints on the density of defects from various experiments. © 2013 American Physical Society. Source

Caspeta L.,Chalmers University of Technology | Chen Y.,Chalmers University of Technology | Ghiaci P.,Chalmers University of Technology | Feizi A.,Chalmers University of Technology | And 6 more authors.
Science | Year: 2014

Ethanol production for use as a biofuel is mainly achieved through simultaneous saccharification and fermentation by yeast. Operating at ≥40°C would be beneficial in terms of increasing efficiency of the process and reducing costs, but yeast does not grow efficiently at those temperatures. We used adaptive laboratory evolution to select yeast strains with improved growth and ethanol production at ≥40°C. Sequencing of the whole genome, genome-wide gene expression, and metabolic-flux analyses revealed a change in sterol composition, from ergosterol to fecosterol, caused by mutations in the C-5 sterol desaturase gene, and increased expression of genes involved in sterol biosynthesis. Additionally, large chromosome III rearrangements and mutations in genes associated with DNA damage and respiration were found, but contributed less to the thermotolerant phenotype. Source

Hossenfelder S.,KTH Royal Institute of Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

It is explained why the argument by Amelino-Camelia et al. does not answer the question how to describe multiparticle states in models with a deformed Lorentz symmetry in momentum space. © 2013 American Physical Society. Source

Grishin A.M.,KTH Royal Institute of Technology
Applied Physics Letters | Year: 2010

We modeled transmission and Faraday rotation characteristics of Er-doped all-garnet [Bi3 Fe5 O12 / Gd3 Ga5 O12]m photonic crystals in view of their application in C -band magneto-optical amplifiers. It is found that 48 layered 11.4 μm thick crystal at λ=1532 nm provides 45° Faraday rotation and transmission as high as 85% being pumped with 100 mW/980 nm solid state laser diode. © 2010 American Institute of Physics. Source

Hansson S.O.,KTH Royal Institute of Technology
Journal of Risk Research | Year: 2010

Perhaps the most fundamental divide in risk research is that between proponents of two contradictory concepts of risk. Some take risk as objectively given and determined by physical facts, whereas others see risk as a social construction that is independent of physical facts. These two views are scrutinized, and it is concluded that neither is tenable. Risk is both fact-laden and value-laden, and it contains both objective and subjective components. It is argued that both the objectivist and the subjectivist view of risk are failed attempts to rid a complex concept of much of its complexity. The real challenge is to identify the various types of factual and valuational components inherent in statements about risk and to understand how they are combined. The two oversimplifications both stand in the way of a more sophisticated analysis of risk. Source

Wahlstrom J.,KTH Royal Institute of Technology
Tribology International | Year: 2015

Airborne wear particles originating from disc brakes are among the main contributors to non-exhaust emissions. The macroscopic wear behaviour of disc brakes can be explained by the growth and destruction of mesoscopic contact plateaus. The pad wear and temperature has earlier been simulated using a cellular automaton mesoscopic approach. The present paper seeks to refine the simulation approach to include disc wear and temperature, and to investigate the validity of this approach by comparing simulated brake events with a dyno bench test. The comparison shows a promising qualitative correlation between the simulated and the experimental results. © 2015 Elsevier Ltd. All rights reserved. Source

Johansson M.,KTH Royal Institute of Technology
Journal of Rural Studies | Year: 2016

Labour market structures which offer fewer options to women than to men, as well as relatively poor educational facilities, are usually mentioned as primary causes for why remote and economically weak regions are affected by selective out-migration and a shortage of young women. This paper is a spin-off from the ESPON-project SEMIGRA - Selective Migration and Unbalanced Sex Ratio in Rural Regions. Its aim is to analyse the out-migration patterns of young women from the Swedish rural region of Västernorrland - with its dual economic and social character - and contrast it to the migration patterns in the expanding Stockholm. The empirical evidence consists of age-specific gross migration data for cohorts in the ages between 18 and 34.By disaggregating the migratory flows during the period 2000-2014 some contrasting results can be shown. Net out-migration is only a reality in the ages between 18 and 24, while the opposite is true in the ages 25-29 and 30-34. This indicates that the 'problem' of out-migration of young women is connected to the pursuit of education and moving to more female-friendly labour markets. In the household creating ages there seems to be a return-migration flow, with net in-migration as one consequence. In the dualistic region of Västernorrland this was particularly evident, especially in the more densely populated coastal areas. It is also highlighted that immigration of both women and men hamper the population decrease and sometimes also result in population increase even if the internal migration is negative for all communities.The dual character of Västernorrland region is also highlighted, and the differing municipalities and cities are analysed. Here, different migratory patterns amongst young women seem to be related to economic, social, behavioural, and demographic structures that also accentuate the dualistic character if the region. © 2015 Elsevier Ltd. Source

Wiklund M.,KTH Royal Institute of Technology
Lab on a Chip - Miniaturisation for Chemistry and Biology | Year: 2012

Manipulation of biological cells by acoustic radiation forces is often motivated by its improved biocompatibility relative to alternative available methods. On the other hand, it is well known that acoustic exposure is capable of causing damage to tissue or cells, primarily due to heating or cavitation effects. Therefore, it is important to define safety guidelines for the design and operation of the utilized devices. This tutorial discusses the biocompatibility of devices designed for acoustic manipulation of mammalian cells, and different methods for quantifying the cell viability in such devices. © 2012 The Royal Society of Chemistry. Source

Hansson S.O.,KTH Royal Institute of Technology
Process Safety and Environmental Protection | Year: 2010

By inherent safety is meant that a hazard is eliminated rather than being managed by various add-on equipment and procedures. Practices of inherent safety have been developed in the chemical industry, and include for instance the substitution of hazardous substances by less hazardous ones. Inherently safer design strives to eliminate the possibility of major adverse events even when the probabilities of these events are small or cannot be meaningfully estimated. Considerations of security can be more easily incorporated into this approach than into most other branches of risk and safety analysis. Therefore, inherent safety has a great potential as a meeting-ground for the much-needed coordination of safety and security work. Its philosophical underpinnings are outlined, and proposals are made for more efficient promotion of its principles. © 2010 The Institution of Chemical Engineers. Source

Wang L.,KTH Royal Institute of Technology
Journal of Manufacturing Systems | Year: 2015

Small- and medium-sized enterprises (SMEs) in job-shop machining are experiencing more shop-floor uncertainties today than ever before, due to multi-tier outsourcing, customised product demands and shortened product lifecycle. In a fluctuating shop floor environment, a process plan generated in advance is often found unsuitable or unusable to the targeted resources, resulting both in wasted effort spent in early process planning and in productivity drop when idle machines have to wait for operations to be re-planned. Consequently, an adaptive process planning approach is in demand. Targeting shop-floor uncertainty, the objective of this research is to develop a novel adaptive process planning method that can generate process plans at runtime to unplanned changes. This paper, in particular, presents an overview of adaptive process planning research and a new methodology, including two-layer system architecture, generic supervisory planning, machine-specific operation planning, and adaptive setup planning. Particularly, function blocks are introduced as a core enabling technology to bridge the gap between computer systems and CNC systems for adaptive machining. © 2014 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved. Source

Kloo L.,KTH Royal Institute of Technology
Chemical Communications | Year: 2013

This viewpoint describes the background of the development of organic dyes for dye-sensitized solar cells, the impact of the 2006 ChemComm paper by Sun, Hagfeldt and co-workers regarding the D5 D-π-A-family of dyes, some recent developments and possible future challenges to meet. © 2013 The Royal Society of Chemistry. Source

Conroy A.,Lancaster University | Koivisto T.,KTH Royal Institute of Technology | Mazumdar A.,Lancaster University | Teimouri A.,Lancaster University
Classical and Quantum Gravity | Year: 2015

Metric theories of gravity are studied, beginning with a general action that is quadratic in curvature and allows arbitrary inverse powers of the dAlembertian operator, resulting in infrared non-local extensions of general relativity. The field equations are derived in full generality and their consistency is checked by verifying the Bianchi identities. The weak-field limit is computed and a straightforward algorithm is presented to infer the post-Newtonian corrections directly from the action. This is then applied to various infrared gravity models including non-local dark energy and non-local massive gravity models. Generically, the Newtonian potentials are not identical and deviate from the behaviour at large distances. However, the former does not occur in a specific class of theories that does not introduce additional degrees of freedom in flat spacetime. A new non-local model within this class is proposed, defined by the exponential of the inverse dAlembertian. This model exhibits novel features, such as the weakening of the gravity in the infrared, suggesting de-gravitation of the cosmological constant. © 2015 IOP Publishing Ltd. Source

Lundell F.,KTH Royal Institute of Technology | Carlsson A.,University of British Columbia
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2010

The motion of an inertial ellipsoid in a creeping linear shear flow of a Newtonian fluid is studied numerically. This constitutes a fundamental system that is used as a basis for simulations and analysis of flows with heavy nonspherical particles. The torque on the ellipsoid is given analytically by Jeffery. This torque is coupled with the angular-momentum equation for the particle. The motion is then governed by the Stokes number St= ρe γ |2 /μ, where ρe is the density of the ellipsoid, γ is the rate of shear, | is the length of the major axis of the ellipsoid, and μ is the dynamic viscosity of the fluid. For low St (the numerical value depends on the aspect ratio of the particle), the particle motion is similar to the Jeffery orbits obtained for inertia-free particles with the addition of an orbit drift so that the particle eventually lies in the flow-gradient plane. At higher St, more drastic effects are seen. For particles oriented in the flow-gradient plane, the rotation rate increases rather abruptly to half the shear rate in a narrow range of St. For particles with other orientations, the motion goes from a kayaking motion to rotation around an oblique axis. It is suggested that, depending on aspect and density ratios, particle inertia might be sufficient to explain and model orbit drift observed previously at low Reynolds numbers. It is discussed how and when the assumption of negligible fluid inertia and strong particle inertia can be justified from a fundamental perspective for particles of different aspect ratios. © 2010 The American Physical Society. Source

Ding L.,East China University of Science and Technology | Zhang Z.,East China University of Science and Technology | Li X.,KTH Royal Institute of Technology | Su J.,East China University of Science and Technology
Chemical Communications | Year: 2013

Two thioxanthone-based fluorescent probes exhibited prominent solvatofluorochromism, and they were further found to be useful as fluorescence indicators for the qualitative and quantitative detection of low-level water content in various solvent media. © 2013 The Royal Society of Chemistry. Source

Liu K.,KTH Royal Institute of Technology | Fridman E.,Tel Aviv University
Systems and Control Letters | Year: 2014

This paper deals with the solution bounds for time-delay systems via delay-dependent Lyapunov-Krasovskii methods. Solution bounds are widely used for systems with input saturation caused by actuator saturation or by the quantizers with saturation. We show that an additional bound for solutions is needed for the first time-interval, where t<τ(t), both in the continuous and in the discrete time. This first time-interval does not influence on the stability and the exponential decay rate analysis. The analysis of the first time-interval is important for nonlinear systems, e.g., for finding the domain of attraction. Regional stabilization of a linear (probably, uncertain) system with unknown and bounded input delay under actuator saturation is revisited, where the saturation avoidance approach is used. © 2013 Elsevier B.V. All rights reserved. Source

Lourdudoss S.,KTH Royal Institute of Technology
Current Opinion in Solid State and Materials Science | Year: 2012

This article reviews the major achievements in recent years on heteroepitaxy and selective area heteroepitaxy that are relevant to silicon photonics. Material aspects are given due importance without trying to cover all kinds of devices. Under heteroepitaxy several systems based on GaAs, InP and GaSb and their related materials and dilute III-nitrides all on Si substrates are covered and assessed. Quantum dot and quantum well lasers are taken as device examples. The potential of the emerging SnGeSi/Si system is highlighted. Under selective area heteroepitaxy, growth of InP from SiO 2 trenches in Si and epitaxial lateral overgrowth of InP on silicon are exemplified as the potential routes for monolithic integration on silicon. The expected trends and anticipated advances are indicated. © 2012 Elsevier Ltd. All rights reserved. Source

Li Q.,Zhejiang University | Qiu M.,Zhejiang University | Qiu M.,KTH Royal Institute of Technology
Optics Express | Year: 2013

Propagation modes and single-guiding-mode conditions of onedimensional silver nanowires based surface plasmon polariton (SPP) waveguides versus the operating wavelength (500-2000 nm) are investigated. For silver nanowires immersed in a SiO2 matrix, both shortrange SPP (SRSPP)-like modes and long-range SPP (LRSPP)-like modes can be guided. However, only the LRSPP-like modes have cutoff radii. For silver nanowires on a SiO2 substrate, the LRSPP-like modes cannot be supported due to asymmetry. While for the SRSPP-like guiding mode, it has a cutoff radius for wavelength longer than 615 nm. For wavelength shorter than 615 nm, there is no cutoff radius for the guiding modes due to the appearance of the interface modes and thus the single-guiding-mode operation is always satisfied. © 2013 Optical Society of America. Source

Moberg C.,KTH Royal Institute of Technology
Israel Journal of Chemistry | Year: 2012

Chiral ligands and metal complexes with rotational (C n, D n) symmetry often have beneficial properties in asymmetric catalysis. The enhanced enantioselectivity frequently observed is a result of a reduction of competing reaction routes. This may be due to rotational symmetry in the catalyst, leading to a limited number of different catalyst-substrate interactions, or to formation of a limited number of catalytic species as a result of rotational symmetry in the ligand. The effect of symmetry is usually difficult to evaluate, since a change in symmetry properties necessarily is accompanied by structural modifications. In each situation the number of intermediate complexes, their electronic and steric properties, and their energy need to be analyzed. Although other factors may be more important than symmetry for achieving high enantioselectivity, a vast number of C 2- and to some extent C 3-symmetric ligands have been found to have excellent properties in asymmetric catalysis, providing products with high enantiomeric purity. Besides the benefit of symmetry in the ligand and catalyst, the symmetry of the substrate may be important since a gain in enantioselectivity can result from simultaneous asymmetric transformations of homotopic functional groups. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Wang M.,Dalian University of Technology | Chen L.,Dalian University of Technology | Sun L.,Dalian University of Technology | Sun L.,KTH Royal Institute of Technology
Energy and Environmental Science | Year: 2012

This perspective article reviews the recent important progress in electrocatalytic hydrogen production catalyzed by earth-abundant metal complexes. The catalysts are divided into two categories depending on the media used in the hydrogen-evolving reactions, with an emphasis on the types of acids employed. The catalysts used in the first category, which work in organic solutions, include nickel and cobalt complexes with base-containing diphosphine ligands, cobaloximes, cobalt tetrapyridine complexs, and [NiFe]- and [FeFe]-hydrogenase mimics. Molybdenum and cobalt pentapyridine complexes, as well as the cobalt bis(iminopyridine) complex reported very recently, are the most important examples of catalysts used in the second category, which work in aqueous solutions. The advantages and disadvantages of the different types of catalysts are discussed and the hydrogen-evolving mechanisms for the well-studied catalysts are illustrated. In addition, several molecular catalyst-modified electrodes for hydrogen production are described. © 2012 The Royal Society of Chemistry. Source

Amelin M.,KTH Royal Institute of Technology
IEEE Transactions on Power Systems | Year: 2015

Many countries are planning for a large-scale expansion of wind power. This development will have a significant impact on power system operation and economics. One of the challenges is that the difficulty to forecast wind power generation will increase the need for real-time balancing. This paper presents a study of how the impact of wind power forecast errors can be reduced by changes in the market design. The study is based on the conditions in the Nordic electricity market. A characteristic of this market is that there is a large share of flexible hydro generation; hence, ramp and unit commitment constraints rarely constrain dispatch. The need for regulation during real-time is provided in a voluntary real-time balancing market, where players can be compensated for their redispatch costs. Case studies are presented which show that a shift from day-ahead to intraday trading and increased demand response can improve the performance when the share of wind power is increasing. © 2014 IEEE. Source

Meng L.,Zhejiang University | Zhao D.,Zhejiang University | Li Q.,Zhejiang University | Qiu M.,Zhejiang University | Qiu M.,KTH Royal Institute of Technology
Optics Express | Year: 2013

Three different types of polarization-sensitive perfect absorbers are designed and numerically investigated. The bottle-like and the cup-like absorbers are narrowband absorbers, which strongly absorb light of a specific polarization and reflect almost all light of another polarization. By varying the geometric parameters, their absorption peaks can be tuned from 1300 nm to 2300 nm and 700 nm to 1400 nm, respectively. The broadband absorber is polarization-sensitive as well, exhibiting an average absorption efficiency of 88% over a wide range of wavelength (700-2300 nm). The proposed absorbers may have potential applications in polarization detectors, polarizers etc. © 2012 Optical Society of America. Source

Huang Q.,Zhejiang University | Bao F.,Zhejiang University | He S.,Zhejiang University | He S.,KTH Royal Institute of Technology
Optics Express | Year: 2013

The effect of nonlocal optical response is studied for a novel silicon hybrid plasmonic waveguide (HPW). Finite element method is used to implement the hydrodynamic model and the propagation mode is analyzed for a hybrid plasmonic waveguide of arbitrary cross section. The waveguide has an inverted metal nano-rib over a silicon-on-insulator (SOI) structure. An extremely small mode area of ∼10-6 λ2 is achieved together with several microns long propagation distance at the telecom wavelength of 1.55μm. The figure of merit (FoM) is also improved in the same time, compared to the pervious hybrid plasmonic waveguide. We demonstrate the validity of our method by comparing our simulating results with some analytical results for a metal cylindrical waveguide and a metal slab waveguide in a wide wavelength range. For the HPW, we find that the nonlocal effects can give less loss and better confinement. In particular, we explore the influence of the radius of the rib's tip on the loss and the confinement. We show that the nonlocal effects give some new fundamental limitation on the confinement, leaving the mode area finite even for geometries with infinitely sharp tips. © 2013 Optical Society of America. Source

Stankovic M.S.,KTH Royal Institute of Technology | Stipanovic D.M.,University of Illinois at Urbana - Champaign
Automatica | Year: 2010

In this paper the extremum seeking algorithm with sinusoidal perturbations has been extended and modified in two ways: (a) the output of the system is corrupted with measurement noise; (b) the amplitudes of the perturbation signals, as well as the gain of the integrator block, are time varying and tend to zero at a pre-specified rate. Convergence to the extremal point, with probability one, has been proved. Also, as a consequence of being able to cope with a stochastic environment, it has been shown how the proposed algorithm can be applied to mobile sensors as a tool for achieving the optimal observation positions. The proposed algorithm has been illustrated through several simulations. © 2010 Elsevier Ltd. All rights reserved. Source

Bayoglu Flener E.,KTH Royal Institute of Technology
Journal of Bridge Engineering | Year: 2010

The paper presents the static loading of four long-span deep-corrugated steel box culverts with spans of 14 and 8 m. The tests, which were part of a series of full-scale tests, involved strain and displacement measurements carried out at different cover depths under the load of a truck. Two of the culverts were stiffened at the crown. The test results showed that the stiffening applied on the culverts is quite effective and that plain structure is more sensitive to cover depth compared to stiffened structure. The crown stiffening is more effective under shallow soil covers. The maximum displacement of plain structure is approximately twice the maximum displacement of the stiffened structure measured at 45-cm depth of cover. The Swedish and Canadian design methods are conservative when estimating live load moments but they underestimate live load thrusts. The measured maximum thrusts are up to four times larger than the calculated design values where the variation depends on the size of the culverts and the depth of soil. The culvert size has considerable influence on the thrusts and moments generated at the crown centerline, which could be implemented in the design models. © 2010 ASCE. Source

Melinder A.,KTH Royal Institute of Technology
International Journal of Refrigeration | Year: 2010

Indirect systems with aqueous solution have long been used to minimize the charge and leakage of (primary) refrigerants. In ice slurry applications such aqueous solutions are used below the freezing point, benefitting from the enthalpy change resulting from ice melting. Accurate thermophysical property data and a general knowledge of other secondary fluid properties are useful for selection of fluid and for technical calculations of the system. This paper introduces a new IIR publication, Properties of secondary working fluids for indirect systems. Tables and charts with fluid properties, property relations of ice and of ice slurry, enthalpy-phase diagrams and related charts are here given for sodium chloride and water, as an example. This new IIR publication that also considers corrosion aspects and environmental impact of such fluids is intended to be used by industry and researchers working with single phase as well as ice slurry applications. © 2010 Elsevier Ltd and IIR. Source

Mardinoglu A.,Chalmers University of Technology | Nielsen J.,Chalmers University of Technology | Nielsen J.,Technical University of Denmark | Nielsen J.,KTH Royal Institute of Technology
Current Opinion in Biotechnology | Year: 2015

Abnormalities in cellular functions are associated with the progression of human diseases, often resulting in metabolic reprogramming. GEnome-scale metabolic Models (GEMs) have enabled studying global metabolic reprogramming in connection with disease development in a systematic manner. Here we review recent work on reconstruction of GEMs for human cell/tissue types and cancer, and the use of GEMs for identification of metabolic changes occurring in response to disease development. We further discuss how GEMs can be used for the development of efficient therapeutic strategies. Finally, challenges in integration of cell/tissue models for simulation of whole body functions as well as integration of GEMs with other biological networks for generating complete cell/tissue models are presented. © 2014 Elsevier Ltd. Source

Sjoberg L.E.,KTH Royal Institute of Technology
Studia Geophysica et Geodaetica | Year: 2011

Today air-gravimetry is a versatile technique to quickly collect gravity data over large regions, where terrestrial gravity data are sparse and/or of poor quality. The method requires the data to be downward continued to sea level for use in geoid determination, an inverse problem operation that calls for smoothing of the data and/or the kernel function involved (in either spectral or space domain). In this purely theoretical study we avoid this separate computational step by performing direct geoid estimation by so-called spectral combination/filtering of the data, which includes terrestrial gravimetry, airgravimetry, an Earth Gravitational Model (EGM) as well as their signal and error degree variances. Each derived geoid estimator is presented as the sum of one or two integral formulas and the harmonic series of the EGM together with the expected mean square error of the estimator. The article is limited to a theoretical study, leaving its practical tests for future investigation. © 2011 Institute of Geophysics of the ASCR, v.v.i. Source

Jonsson U.T.,KTH Royal Institute of Technology | Kao C.-Y.,National Sun Yat - sen University
IEEE Transactions on Automatic Control | Year: 2010

A scalable robust stability criterion for interconnected systems with heterogeneous linear time-invariant components is presented in this paper. The criterion involves only the properties of individual components and the spectrum of the interconnection matrix, which can be verified with relatively low computational effort, and more importantly maintains scalability of the analysis. Our main result shows that if the components are single-input-single- output (SISO), then the criterion has an appealing graphical interpretation which resembles the classical Nyquist criterion. © 2010 IEEE. Source

Alsafadie R.,INSA Rennes | Hjiaj M.,INSA Rennes | Battini J.-M.,KTH Royal Institute of Technology
Computer Methods in Applied Mechanics and Engineering | Year: 2010

The corotational technique is adopted here for the analysis of three-dimensional beams. The technique exploits the technology that applies to a two-noded element, a coordinate system which continuously translates and rotates with the element. In this way, the rigid body motion is separated out from the deformational motion. In this paper, a mixed formulation are adopted for the derivation of the local element tangent stiffness matrix and nodal forces. The mixed finite element formulation is based on an incremental form of the two-field Hellinger-Reissner variational principle to permit elasto-plastic material behavior. The local beam kinematics is based on a low-order nonlinear strain expression using Bernoulli assumption. The present formulation captures both the Saint-Venant and warping torsional effects of thin-walled open cross-sections. Shape functions that satisfy the nonlinear local equilibrium equations are selected for the interpolation of the stress resultants. In particular, for the torsional forces and the twist rotation degree of freedom, a family of hyperbolic interpolation functions is adopted in lieu of conventional polynomials. Governing equations are expressed in a weak form, and the constitutive equations are enforced at each integration cross-section along the element length. A consistent state determination algorithm is proposed. This local element, together with the corotational framework, can be used to analyze the nonlinear buckling and postbuckling of thin-walled beams with generic cross-section. The present corotational mixed element solution is compared against the results obtained from a corotational displacement-based model having the same beam kinematics and corotational framework. The superiority of the mixed formulation is clearly demonstrated. © 2010 Elsevier B.V. Source

Siebentritt S.,University of Luxembourg | Igalson M.,Warsaw University of Technology | Persson C.,KTH Royal Institute of Technology | Lany S.,National Renewable Energy Laboratory
Progress in Photovoltaics: Research and Applications | Year: 2010

We summarize the progress made recently in understanding the electronic structure of chalcopyrites. New insights into the dispersion of valence and conduction band allow conclusions on the effective masses of charge carriers and their orientation dependence, which influences the transport in solar cell absorbers of different orientation. Native point defects are responsible for the doping and thus the band bending in solar cells. Results of optoelectronic defect spectroscopy are reviewed. Native defects are also the source for a number of metastabilities, which strongly affect the efficiency of solar cells. Recent theoretical findings relate these effects to the Se vacancy and the InCu antisite defect. Experimentally determined activation energies support these models. Absorbers in chalcopyrite solar cells are polycrystalline, which is only possible because of the benign character of the grain boundaries. This can be related to an unusual electronic structure of the GB. Copyright © 2010 John Wiley & Sons, Ltd. Source

Blanchet L.,University Pierre and Marie Curie | Heisenberg L.,KTH Royal Institute of Technology | Heisenberg L.,The Oskar Klein Center
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

In this work we investigate the existence of relativistic models for dark matter in the context of bimetric gravity, used here to reproduce the modified Newtonian dynamics (MOND) at galactic scales. For this purpose we consider two different species of dark matter particles that separately couple to the two metrics of bigravity. These two sectors are linked together via an internal U(1) vector field, and some effective composite metric built out of the two metrics. Among possible models only certain classes of kinetic and interaction terms are allowed without invoking ghost degrees of freedom. Along these lines we explore the number of allowed kinetic terms in the theory and point out the presence of ghosts in a previous model. Finally, we propose a promising class of ghost-free candidate theories that could provide the MOND phenomenology at galactic scales while reproducing the standard cold dark matter model at cosmological scales. © 2015 American Physical Society. Source

Olshevsky V.,Catholic University of Leuven | Lapenta G.,Catholic University of Leuven | Markidis S.,KTH Royal Institute of Technology
Physical Review Letters | Year: 2013

We perform three-dimensional particle-in-cell simulations of magnetic reconnection with multiple magnetic null points. Magnetic field energy conversion into kinetic energy is about five times higher than in traditional Harris sheet configuration. More than 85% of initial magnetic field energy is transferred to particle energy during 25 reversed ion cyclofrequencies. Magnetic reconnection in the cluster of null points evolves in three phases. During the first phase, ion beams are excited, then give part of their energy back to the magnetic field in the second phase. In the third phase, magnetic reconnection occurs in many small patches around the current channels formed along the stripes of a low magnetic field. Magnetic reconnection in null points essentially presents three-dimensional features, with no two-dimensional symmetries or current sheets. © 2013 American Physical Society. Source

Murugan N.A.,KTH Royal Institute of Technology
Journal of Physical Chemistry B | Year: 2011

We have investigated the ambient temperature structure of 1-methyl-8-oxyquinolinium betaine (MOQB) in water solvent and compared to its gas-phase structure. We have employed Car-Parrinello molecular dynamics (CPMD) simulations within hybrid quantum mechanics-molecular mechanics (QM/MM) framework to study MOQB in water while CPMD technique has been used for the gas phase. We report significant solvent-induced geometrical changes in MOQB. The dipole moment of MOQB in water is 2 times larger than the gas-phase value. The average absorption spectra calculated from gas-phase configurations using Coulomb attenuated-B3LYP (CAMB3LYP) level of theory is comparable with experimental spectra reported in benzene (λmax = 590 nm), a nonpolar solvent. We have also computed the absorption spectra of MOQB in water solvent using continuum and semicontinuum solvent models. Based on this, we have calculated contributions from solvent-induced geometrical changes, hydrogen bonding, and intermolecular charge transfer to the solvatochromic shift and absorption spectra of MOQB in water. Absorption spectra calculations for MOQB in water with a semicontinuum approach for solvents using CAMB3LYP level of theory excellently reproduce the experimental spectra in water, where the theoretical λmax is 433 nm and the experimental λmax is around 440 nm. © 2011 American Chemical Society. Source

Fransson J.H.M.,KTH Royal Institute of Technology
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2010

A demanding task, for successful fluid dynamic design in many industrial applications, is being able to predict the transition to turbulence location in boundary layer flows. The focus of the present experimental study is on the late stage of transition scenarios where turbulent spots are borne. We report on a natural stabilizing mechanism on the growth rate of turbulent spots, which takes place in a specific bypass transition scenario, and show that there is a palpable history effect of the origin of the turbulent spot on the streamwise evolution. Furthermore, experimental evidence on Reynolds number effects on the spot evolution in boundary layers is put forward. This has been made possible by setting up an idealized experiment, which usually only is considered as a schoolbook example. © 2010 The American Physical Society. Source

Davison R.A.,Lorentz Institute for Theoretical Physics | Gouteraux B.,KTH Royal Institute of Technology | Gouteraux B.,Stanford University | Gouteraux B.,University of Paris Pantheon Sorbonne
Journal of High Energy Physics | Year: 2015

Abstract: We study heat transport in two systems without momentum conservation: a hydrodynamic system, and a holographic system with spatially dependent, massless scalar fields. When momentum dissipates slowly, there is a well-defined, coherent collective excitation in the AC heat conductivity, and a crossover between sound-like and diffusive transport at small and large distance scales. When momentum dissipates quickly, there is no such excitation in the incoherent AC heat conductivity, and diffusion dominates at all distance scales. For a critical value of the momentum dissipation rate, we compute exact expressions for the Green’s functions of our holographic system due to an emergent gravitational self-duality, similar to electric/magnetic duality, and SL(2,ℝ) symmetries. We extend the coherent/incoherent classification to examples of charge transport in other holographic systems: probe brane theories and neutral theories with non-Maxwell actions. © 2015, The Author(s). Source

Eshagh M.,KTH Royal Institute of Technology
Acta Geophysica | Year: 2011

Solution of the gradiometric boundary value problems leads to three integral formulas. If we are satisfied with obtaining a smooth solution for the Earth's gravity field, we can use the formulas in regional gravity field modelling. In such a case, satellite gradiometric data are integrated on a sphere at satellite level and continued downward to the disturbing potential (geoid) at sea level simultaneously. This paper investigates the gravity field modelling from a full tensor of gravity at satellite level. It studies the truncation bias of the integrals as well as the filtering of noise of data. Numerical studies show that by integrating Tzz with 1 mE noise and in a cap size of 7°, the geoid can be recovered with an error of 12 cm after the filtering process. Similarly, the errors of the recovered geoids from Txz,yz and Txx-yy, 2xy are 13 and 21 cm, respectively. © 2010 Versita Warsaw and Springer-Verlag Wien. Source

Dargahi B.,KTH Royal Institute of Technology
Journal of Hydraulic Research | Year: 2010

This study investigates the discharge characteristics of a bottom outlet with a moving gate by Flow3D. Experimental results for a scale model outlet of the Aswan Dam, Egypt, were used. Two different flow features were found. Pressurized flow established if the flume was filled and then the gate was slowly opened. However, a free surface flow occurred if the gate was fully opened and the entire flume was slowly flooded with water. The numerical simulations successfully captured the two flow patterns as well as the discharges and water surface profiles. The discharges were predicted with sufficient accuracy using the first-order momentum advection scheme. In comparison with the k-turbulence model, the Re-Normalization Group model yields the best agreement with the experiments. The model performed with similar accuracy for both model and prototype cases. © 2010 International Association for Hydro-Environment Engineering and Research. Source

Eshagh M.,KTH Royal Institute of Technology
Contributions to Geophysics and Geodesy | Year: 2010

Errors of estimated parameters in an adjustment process should be scaled according to the size of the estimated residuals or misclosures. After computing a quasigeoid (geoid), its biases and tilts, due to existence of systematic errors in the terrestrial data, are removed by fitting a corrective surface to the misclosures of the differences between the GNSS/levelling data and the quasi-geoid (geoid). Variance component estimation can be used to re-scale or calibrate the error of the GNSS/levelling data and the quasi-geoid (geoid) model. This paper uses this method to calibrate the errors of the recent quasi-geoid model, the GNSS and the normal heights of Sweden. Different stochastic models are investigated in this study and based on a 7-parameter corrective surface model and a three-variance component stochastic model, the calibrated error of the quasi-geoid and the normal heights are 6 mm and 5 mm, respectively and the re-scaled error of the GNSS heights is 18 mm. Source

Wester M.,KTH Royal Institute of Technology
Journal of Contingencies and Crisis Management | Year: 2011

This article reports on how professionals at municipal level responsible for crisis communication (N=152) in Sweden judge the probability of 10 different responses occurring among the public, among people within their own emergency organization and themselves in case of a crisis. The direct physical effects of the crisis were kept identical throughout the study, but the cause of the crisis varied over three scenarios: accidental, terrorist and unknown. The results show that there are differences between how the respondents judge the reactions of themselves, their peers and the public, and there are also differences in the three crisis presented. The respondents judged their own reactions to be more logical and rational, and less marked by fear, panic and irrationality compared with the other two groups in all three crises. Also, it was investigated what source of information the crisis communicators thought would be used most by the public. The perceived sources of information varied depending on the cause of the crisis. The merit of these assumptions and implications for crisis communication are discussed. © 2011 Blackwell Publishing Ltd. Source

Kutcherov V.G.,KTH Royal Institute of Technology | Krayushkin V.A.,Ukrainian Academy of Sciences
Reviews of Geophysics | Year: 2010

The theory of the abyssal abiogenic origin of petroleum is a significant part of the modern scientific theories dealing with the formation of hydrocarbons. These theories include the identification of natural hydrocarbon systems, the physical processes leading to their terrestrial concentration, and the dynamic processes controlling the migration of that material into geological reservoirs of petroleum. The theory of the abyssal abiogenic origin of petroleum recognizes that natural gas and petroleum are primordial materials of deep origin which have migrated into the Earth's crust. Experimental results and geological investigations presented in this article convincingly confirm the main postulates of the theory and allow us to reexamine the structure, size, and locality distributions of the world's hydrocarbon reserves. Copyright © 2010 by the American Geophysical Union. Source

Auer M.,Vascops GmbH | Gasser T.C.,KTH Royal Institute of Technology
IEEE Transactions on Medical Imaging | Year: 2010

Evaluating rupture risk of abdominal aortic aneurysms is critically important in reducing related mortality without unnecessarily increasing the rate of elective repair. According to the current clinical practice aneurysm rupture risk is (mainly) estimated from its maximum diameter and/or expansion rate; an approach motivated from statistics but known to fail often in individuals. In contrast, recent research demonstrated that patient specific biomechanical simulations can provide more reliable diagnostic parameters, however current structural model development is cumbersome and time consuming. This paper used 2D and 3D deformable models to reconstruct aneurysms from computerized tomography angiography data with minimal user interactions. In particular, formulations of frames and shells, as known from structural mechanics, were used to define deformable modes, which in turn allowed a direct mechanical interpretation of the applied set of reconstruction parameters. Likewise, a parallel finite element implementation of the models allows the segmentation of clinical cases on standard personal computers within a few minutes. The particular topology of the applied 3D deformable models supports a fast and simple hexahedral-dominated meshing of the arising generally polyhedral domain. The variability of the derived segmentations (luminal: 0.50(SD 0.19) mm; exterior 0.89(SD 0.45) mm) with respect to large variations in elastic properties of the deformable models was in the range of the differences between manual segmentations as performed by experts (luminal: 0.57(SD 0.24) mm; exterior: 0.77(SD 0.58) mm), and was particularly independent from the algorithm's initialization. The proposed interaction of deformable models and mesh generation defines finite element meshes suitable to perform accurate and efficient structural analysis of the aneurysm using mixed finite element formulations. © 2006 IEEE. Source

Ahlquist M.S.G.,KTH Royal Institute of Technology
Journal of Molecular Catalysis A: Chemical | Year: 2010

A density functional theory study of the mechanism of the iridium catalyzed hydrogenation of carbon dioxide is presented. The rate-limiting step is found to be the regeneration of the iridium(III) trihydride. © 2010 Elsevier B.V. All rights reserved. Source

Hansson S.O.,KTH Royal Institute of Technology
Artificial Intelligence | Year: 2014

Relations of epistemic proximity are closely related to relations of epistemic entrenchment, but contrary to the latter they do not refer to sentences but to belief patterns that are expressed with a metalinguistic belief predicate B. Hence ¬Bp≻B¬q means that disbelief in p is more close at hand (obtainable with less far-reaching changes in belief) than belief in not-q. The logic of epistemic proximity is investigated, and it is used to construct a uniform operation of belief change that has the standard operations as special cases, specified with success conditions such as Bp for revision and {¬Bp1,⋯,¬Bpn} for multiple contraction. Standard entrenchment relations are obtained by defining p to be less entrenched than q if and only if ¬Bp≻¬Bq. © 2014 Published by Elsevier B.V. Source

Rathi V.,KTH Royal Institute of Technology | Andriyanova I.,Cergy-Pontoise University
IEEE Transactions on Information Theory | Year: 2011

In this paper, the transmission over the binary erasure channel (BEC) using non-binary LDPC (NBLDPC) codes is considered. The concept of peeling decoder and stopping sets is generalized to NBLDPC codes. Using these generalizations, a combinatorial characterization of decoding failures of NBLDPC codes is given, under assumption that the Belief Propagation (BP) decoder is used. Then, the residual ensemble of codes resulted by the BP decoder is defined and the design rate and the expectation of total number of codewords of the residual ensemble are computed. The decoding failure criterion combined with the density evolution analysis helps us to compute the asymptotic residual degree distribution for NBLDPC codes. Our approach to compute the residual degree distribution on the check node side is not efficient as it is based on enumeration of all the possible connections on the check node side which satisfy the decoding failure criterion. So, the computation of the asymptotic check node side residual degree distribution and further part of our analysis is performed for NBLDPC codes over GF2m with m=2. In order to show that asymptotically almost every code in such LDPC ensemble has a rate equal to the design rate, we generalize the argument of the Maxwell construction to NBLDPC codes, defined over GF22. It is also observed that, like in the binary setting, the Maxwell construction, relating the performance of MAP and BP decoding holds in this setting. © 2011 IEEE. Source

Qi C.,KTH Royal Institute of Technology
Progress of Theoretical Physics Supplement | Year: 2012

The recently proposed spin-aligned neutron-proton pair coupling scheme is studied within a non-orthogonal basis in term of the multistep shell model. This also allows us to identify simultaneously the roles played by different configurations such as the normal pairing term. Source

Bohg J.,Systems In Motion | Morales A.,Jaume I University | Asfour T.,Karlsruhe Institute of Technology | Kragic D.,KTH Royal Institute of Technology
IEEE Transactions on Robotics | Year: 2014

We review the work on data-driven grasp synthesis and the methodologies for sampling and ranking candidate grasps. We divide the approaches into three groups based on whether they synthesize grasps for known, familiar, or unknown objects. This structure allows us to identify common object representations and perceptual processes that facilitate the employed data-driven grasp synthesis technique. In the case of known objects, we concentrate on the approaches that are based on object recognition and pose estimation. In the case of familiar objects, the techniques use some form of a similarity matching to a set of previously encountered objects. Finally, for the approaches dealing with unknown objects, the core part is the extraction of specific features that are indicative of good grasps. Our survey provides an overview of the different methodologies and discusses open problems in the area of robot grasping. We also draw a parallel to the classical approaches that rely on analytic formulations. © 2013 IEEE. Source

The gravity anomalies at sea level can be used to validate the satellite gravity gradiometry data. Validation of such a data is important prior to downward continuation because of amplification of the data errors through this process. In this paper the second-order radial derivative of the extended Stokes' formula is employed and the emphasis is on least-squares modification of this formula to generate the second-order radial gradient at satellite level. Two methods in this respect are proposed: (a) modifying the second-order radial derivative of extended Stokes' formula directly, and (b) modifying extended Stokes' formula prior to taking the second-order radial derivative. Numerical studies show that the former method works well but the latter is very sensitive to the proper choice of the cap size of integration and degree of modification. © 2009 Elsevier Ltd. All rights reserved. Source

Cvetkovic V.,KTH Royal Institute of Technology
Water Resources Research | Year: 2011

The self-purifying capacity of aquifers strongly depends on the attenuation of waterborne contaminants, i.e., irreversible loss of contaminant mass on a given scale as a result of coupled transport and transformation processes. A general formulation of tracer attenuation in groundwater is presented. Basic sensitivities of attenuation to macrodispersion and retention are illustrated for a few typical retention mechanisms. Tracer recovery is suggested as an experimental proxy for attenuation. Unique experimental data of tracer recovery in crystalline rock compare favorably with the theoretical model that is based on diffusion-controlled retention. Non-Fickian hydrodynamic transport has potentially a large impact on field-scale attenuation of dissolved contaminants. Copyright 2011 by the American Geophysical Union. Source

Eshagh M.,KTH Royal Institute of Technology
Acta Geophysica | Year: 2010

The traditional expressions for gravity gradients in local north-oriented frame and tensor spherical harmonics have complicated forms involved with first- and second-order derivatives of spherical harmonics and also singular terms. In this paper we present alternative expressions for these quantities, which are simpler and contain no singular terms. The presented formulas are useful for those disciplines of geosciences which are involved with potential theory, tensor spherical harmonics and second-order derivatives of spherical harmonic series in the local north-oriented frame. A simple numerical test on the solution of the gradiometric boundary value problems presents the correctness of these new expressions and ability of the solutions to continue the gravity gradients from satellite level down to sea level using spherical harmonics. © 2009 Versita Warsaw and Springer-Verlag Berlin Heidelberg. Source

Vanfretti L.,KTH Royal Institute of Technology | Milano F.,University of Castilla - La Mancha
IEEE Transactions on Education | Year: 2012

This paper describes how the use of free and open-source software (FOSS) can facilitate the application of constructive alignment theory in power systems engineering education by enabling the deep learning approach in power system analysis courses. With this aim, this paper describes the authors' approach in using the Power System Analysis Toolbox (PSAT) for undergraduate and graduate education. Interviews with former students reveal the positive impact that the use of FOSS in general, and PSAT in particular, had on their learning and how it has influenced their professional life. © 1963-2012 IEEE. Source

Karasalo M.,Saab | Hu X.,KTH Royal Institute of Technology
Automatica | Year: 2011

In this paper, an optimization-based adaptive Kalman filtering method is proposed. The method produces an estimate of the process noise covariance matrix Q by solving an optimization problem over a short window of data. The algorithm recovers the observations h(x) from a system x=f(x),y=h(x)+v without a priori knowledge of system dynamics. Potential applications include target tracking using a network of nonlinear sensors, servoing, mapping, and localization. The algorithm is demonstrated in simulations on a tracking example for a target with coupled and nonlinear kinematics. Simulations indicate superiority over a standard MMAE algorithm for a large class of systems. © 2011 Elsevier Ltd. All rights reserved. Source

Rizzi A.,KTH Royal Institute of Technology
Progress in Aerospace Sciences | Year: 2011

This paper overviews the SimSAC Project, Simulating Aircraft Stability And Control Characteristics for Use in Conceptual Design. It reports on the three major tasks: development of design software, validating the software on benchmark tests and applying the software to design exercises. CEASIOM, the Computerized Environment for Aircraft Synthesis and Integrated Optimization Methods, is a framework tool that integrates discipline-specific tools for conceptual design. At this early stage of the design it is very useful to be able to predict the flying and handling qualities of this design. In order to do this, the aerodynamic database needs to be computed for the configuration being studied, which then has to be coupled to the stability and control tools to carry out the analysis. The benchmarks for validation are the F12 windtunnel model of a generic long-range airliner and the TCR windtunnel model of a sonic-cruise passenger transport concept. The design, simulate and evaluate (DSE) exercise demonstrates how the software works as a design tool. The exercise begins with a design specification and uses conventional design methods to prescribe a baseline configuration. Then CEASIOM improves upon this baseline by analyzing its flying and handling qualities. Six such exercises are presented. © 2011 Elsevier Ltd. All rights reserved. Source

Ambuhl C.,University of Liverpool | Mastrolilli M.,IDSIA | Svensson O.,KTH Royal Institute of Technology
SIAM Journal on Computing | Year: 2011

We consider the Minimum Linear Arrangement problem and the (Uniform) Sparsest Cut problem. So far, these two notorious NP-hard graph problems have resisted all attempts to prove inapproximability results. We show that they have no polynomial time approximation scheme, unless NP-complete problems can be solved in randomized subexponential time. Furthermore, we show that the same techniques can be used for the Maximum Edge Biclique problem, for which we obtain a hardness factor similar to previous results but under a more standard assumption. Copyright © by SIAM. Source

Brostrom A.,KTH Royal Institute of Technology
Journal of Technology Transfer | Year: 2012

R&D managers at 50 firms who have formal relations with two research universities in Stockholm are interviewed about their rationales for collaboration. Drawing on this material, a distinctive typology of rationales for establishing cooperative relations is presented. While the typology demonstrates a considerable breadth of interaction rationales, rationales related to innovation, in terms of invented or improved products or processes, are found to be the main drivers for interaction. Based on this framework, we analyse which rationales for interaction are consistent with public rationales for supporting university-industry relationships. Public co-funding that allow firms to influence (part of) the academic agenda is identified as a particularly interesting case that requires further theoretical attention. © 2010 Springer Science+Business Media, LLC. Source

Hosseinzadeh N.,Swinburne University of Technology | Hesamzadeh M.R.,KTH Royal Institute of Technology
IEEE Transactions on Education | Year: 2012

Project-based learning (PBL), a learning environment in which projects drive learning, has been successfully used in various courses in the educational programs of different disciplines. However, concerns have been raised as to the breadth of the content covered and, in particular, whether PBL can be applied to specialized subjects without compromising the coverage of the required technical content. This paper discusses the advantages and drawbacks of using the PBL methodology in teaching specialized subjects in electrical power engineering, based on the authors' reflections and student feedback. The design and delivery of a PBL-based course in power system modeling and analysis is used as an example. It is asserted that proper usage of PBL makes it possible to deliver both technical content and generic professional skills in a specialized course. © 2012 IEEE. Source

Belonoshko A.B.,KTH Royal Institute of Technology
Condensed Matter Physics | Year: 2010

The equation of state for hexagonal close packed (hcp or ∈) phase of Fe at high pressure is created by employing molecular dynamics (MD) simulations in conjunction with the embedded atom method based on the full potential linear muffin tin orbital (FPLMTO) method. Comparison between the existing experimental data and our calculations suggests that the obtained equation of state can be reliably used for calculating iron volumetric properties under conditions appropriate for the Earth's core. We demonstrate that some experimental data on iron might be subjected to a systematic error. I suggest a model which describes the temperature dependence of the volume better than the Mie-Grüneisen equation. © A.B. Belonoshko. Source

Garcia-Gallego S.,University of Cambridge | Bernardes G.J.L.,University of Cambridge | Bernardes G.J.L.,University of Lisbon | Bernardes G.J.L.,KTH Royal Institute of Technology
Angewandte Chemie - International Edition | Year: 2014

The development of carbon-monoxide-releasing molecules (CORMs) as pharmaceutical agents represents an attractive and safer alternative to administration of gaseous CO. Most CORMs developed to date are transition-metal carbonyl complexes. Although such CORMs have showed promising results in the treatment of a number of animal models of disease, they still lack the necessary attributes for clinical development. Described in this Minireview are the methods used for CORM selection, to date, and how new insights into the reactivity of metal-carbonyl complexes in vivo, together with advances in methods for live-cell CO detection, are driving the design and synthesis of new CORMs, CORMs that will enable controlled CO release in vivo in a spatial and temporal manner without affecting oxygen transport by hemoglobin. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Sakovich A.,KTH Royal Institute of Technology
Classical and Quantum Gravity | Year: 2010

We follow the approach employed by Y Choquet-Bruhat, J Isenberg and D Pollack in the case of closed manifolds and establish existence and nonexistence results for constant mean curvature solutions of the Einstein-scalar field constraint equations on asymptotically hyperbolic manifolds. © 2010 IOP Publishing Ltd. Source

Qi C.,KTH Royal Institute of Technology
Physical Review C - Nuclear Physics | Year: 2010

For systems with three and four fermions within a single-j shell, analytical expressions for the state energies are presented from a decomposition of the angular momentum. In some important cases the expressions acquire a very simple form. The expression may help us in understanding the structure of isomeric states. The decomposition also makes it possible to construct the algebraic condition for conservation of seniority. © 2010 The American Physical Society. Source

Granryd E.,KTH Royal Institute of Technology
International Journal of Refrigeration | Year: 2010

The flow velocities on the air or liquid side of evaporators and condensers in refrigerating or heat pump systems affect the system performance considerably. Furthermore the velocity can often be chosen rather freely without obvious first cost implications. The purpose of the paper is to show analytical relations indicating possible optimum operating conditions. Considering a base case where the design data are known, simple analytical relations are deduced for optimum flow rates that will result in highest overall COP of the system when energy demand for the compressor as well as pumps or fans are included. This optimum is equivalent to the solution for minimum total energy demand of the system for a given cooling load. It is also shown that a different (and higher) flow rate will result in maximum net cooling capacity for a refrigerating system with fixed compressor speed. The expressions can be used for design purposes as well as for checking suitable flow velocities in existing plants. The relations may also be incorporated in algorithms for optimal operation of systems with variable speed compressors. © 2010 Elsevier Ltd and IIR. All rights reserved. Source

Zhang H.,KTH Royal Institute of Technology | Shen H.,University of Adelaide
IEEE Transactions on Parallel and Distributed Systems | Year: 2010

Geographic routing is an attractive localized routing scheme for wireless sensor networks (WSNs) due to its desirable scalability and efficiency. Maintaining neighborhood information for packet forwarding can achieve a high efficiency in geographic routing, but may not be appropriate for WSNs in highly dynamic scenarios where network topology changes frequently due to nodes mobility and availability. We propose a novel online routing scheme, called Energy-efficient Beaconless Geographic Routing (EBGR), which can provide loop-free, fully stateless, energy-efficient sensor-to-sink routing at a low communication overhead without the help of prior neighborhood knowledge. In EBGR, each node first calculates its ideal next-hop relay position on the straight line toward the sink based on the energy-optimal forwarding distance, and each forwarder selects the neighbor closest to its ideal next-hop relay position as the next-hop relay using the Request-To-Send/Clear-To-Send (RTS/CTS) handshaking mechanism. We establish the lower and upper bounds on hop count and the upper bound on energy consumption under EBGR for sensor-to-sink routing, assuming no packet loss and no failures in greedy forwarding. Moreover, we demonstrate that the expected total energy consumption along a route toward the sink under EBGR approaches to the lower bound with the increase of node deployment density. We also extend EBGR to lossy sensor networks to provide energy-efficient routing in the presence of unreliable communication links. Simulation results show that our scheme significantly outperforms existing protocols in wireless sensor networks with highly dynamic network topologies. © 2006 IEEE. Source

Jena N.K.,Albanova University Center | Murugan N.A.,KTH Royal Institute of Technology
Journal of Physical Chemistry C | Year: 2013

Motion is an essential and fundamental feature of any living organism. The evolved organisms have developed sophisticated and perfect machineries and highly delicate mechanisms to carry out directional and coordinated movements which eventually lead to motion at the macroscopic length scale. By mimicking these natural machineries, attempts to design and synthesize similar molecular motors are made in relevance to their applications in drug delivery, data storage, and molecular sensing. It is highly desirable to establish the rules for controlling the conformational states of molecular motors by tuning some of the external variables which can be used for the design strategies. We contribute to this subject by looking into the solvent influence on the conformational states of a synthetic molecular rotor, namely, diketopyrrolopyrrole (DPP) based [2]rotaxane, using the force-field molecular dynamics approach. We study this system in three different solvents, and we report a strong solvent dependence in the population of three different translational isomers. In chloroform solvent we report the dominant population of the 2-P isomer which is in excellent agreement with experimental results based on H NMR spectra (Org. Lett. 2013, 15, 1274). However, there is a striking difference seen in the population of translational isomers in DMSO solvent, and we attribute these features to negligence of solvent hydrogen bonding induced upfield and downfield effects in the interpretation of experimental proton NMR spectra. In addition, we also report a solvent-polarity-induced fully unstretched to folded conformational transition in the [2]rotaxane system. On the basis of the molecular mechanics Poisson-Boltzmann (and generalized Born) surface area approach, we identify the driving force for the formation of the supramolecular guest-host [2]rotaxane system. Finally, we calculate the relative binding free energies for the macrocycle at different binding sites of the DPP skeleton using the molecular dynamics simulations performed for the macrocycle-rotaxane system in water solvent which suggests the increased stability of the 2-O isomer in polar solvent. © 2013 American Chemical Society. Source

Ranstad P.,Alstom | Nee H.-P.,KTH Royal Institute of Technology
IEEE Transactions on Power Electronics | Year: 2011

Two different dynamic effects influencing the insulated gate bipolar transistor (IGBT) losses in soft-switching converters are demonstrated. The first one, the Dynamic tail-charge effect shows that the tail charge is dependent not only on the absolute value of the current at turn-off, but also on the dynamics of the current. This effect may have a significant impact on the optimization of zero-current-switching converters. The Dynamic conduction losses originate from the conductivity modulation lag of the IGBT. It is shown by experiments that the on-state losses depend on the operating frequency. Different methods to accurately determine the on-state losses are evaluated. It was found that the best method is an indirect measurement, where the stray inductance is identified by the use of an oscillating circuit. The experiments are performed under a sinusoidal current excitation at a fixed amplitude (150 A) for different frequencies (up to 104 kHz). The switching devices used are IGBT modules rated 300-400 A/1200 V in a bridge-leg configuration. From the experiments performed, it is found that IGBTs of a modern punch-though (PT) designs have the lowest losses in the series-loaded resonant converters studied in this paper. © 2006 IEEE. Source

Lindeberg T.,KTH Royal Institute of Technology
Journal of Mathematical Imaging and Vision | Year: 2016

We present an improved model and theory for time-causal and time-recursive spatio-temporal receptive fields, obtained by a combination of Gaussian receptive fields over the spatial domain and first-order integrators or equivalently truncated exponential filters coupled in cascade over the temporal domain. Compared to previous spatio-temporal scale-space formulations in terms of non-enhancement of local extrema or scale invariance, these receptive fields are based on different scale-space axiomatics over time by ensuring non-creation of new local extrema or zero-crossings with increasing temporal scale. Specifically, extensions are presented about (i) parameterizing the intermediate temporal scale levels, (ii) analysing the resulting temporal dynamics, (iii) transferring the theory to a discrete implementation in terms of recursive filters over time, (iv) computing scale-normalized spatio-temporal derivative expressions for spatio-temporal feature detection and (v) computational modelling of receptive fields in the lateral geniculate nucleus (LGN) and the primary visual cortex (V1) in biological vision. We show that by distributing the intermediate temporal scale levels according to a logarithmic distribution, we obtain a new family of temporal scale-space kernels with better temporal characteristics compared to a more traditional approach of using a uniform distribution of the intermediate temporal scale levels. Specifically, the new family of time-causal kernels has much faster temporal response properties (shorter temporal delays) compared to the kernels obtained from a uniform distribution. When increasing the number of temporal scale levels, the temporal scale-space kernels in the new family do also converge very rapidly to a limit kernel possessing true self-similar scale-invariant properties over temporal scales. Thereby, the new representation allows for true scale invariance over variations in the temporal scale, although the underlying temporal scale-space representation is based on a discretized temporal scale parameter. We show how scale-normalized temporal derivatives can be defined for these time-causal scale-space kernels and how the composed theory can be used for computing basic types of scale-normalized spatio-temporal derivative expressions in a computationally efficient manner. © 2015, The Author(s). Source

Hossenfelder S.,KTH Royal Institute of Technology
Advances in High Energy Physics | Year: 2014

Whether or not space-time is fundamentally discrete is of central importance for the development of the theory of quantum gravity. If the fundamental description of spacetime is discrete, typically represented in terms of a graph or network, then the apparent smoothness of geometry on large scales should be imperfect - it should have defects. Here, we review a model for space-time defects and summarize the constraints on the prevalence of these defects that can be derived from observation. © 2014 Sabine Hossenfelder. Source

Recently, much attention has been given to the influence of airborne particles in the atmosphere on human health. Sliding contacts are a significant source of airborne particles. In this study airborne particles from railway block brakes are studied using cast iron and composite block material on railway wheel steel. A pin-on-disc tribometer equipped with airborne particle counting instrumentation was used as experimental set-up. The result shows differences for the two tested block brake material combinations in particle size distribution, morphology and elemental content. © 2010 Elsevier B.V. Source

Barsoum I.,The Petroleum Institute | Faleskog J.,KTH Royal Institute of Technology
International Journal of Solids and Structures | Year: 2011

A micromechanical model consisting of a band with a square array of equally sized cells, with a spherical void located in each cell, is developed. The band is allowed a certain inclination and the periodic arrangement of the cells allow the study of a single unit cell for which fully periodic boundary conditions are applied. The model is based on the theoretical framework of plastic localization and is in essence the micromechanical model by Barsoum and Faleskog (Barsoum, I.; Faleskog, J.; 2007. Rupture mechanisms in combined tension and shear - micromechanics. International Journal of Solids and Structures 44(17), 5481-5498) with the extension accounting for the band orientation. The effect of band inclination is significant on the strain to localization and cannot be disregarded. The macroscopic stress state is characterized by the stress triaxiality and the Lode parameter. The model is used to investigate the influence of the stress state on void growth and coalescence. It is found that the Lode parameter exerts a strong influence on the void shape evolution and void growth rate as well as the localized deformation behavior. At high stress triaxiality level the influence of the Lode parameter is not as marked and the overall ductility is set by the stress triaxiality. For a dominating shear stress state localization into a band cannot be regarded as a void coalescence criterion predicting material failure. A coalescence criterion operative at dominating shear stress state is needed. © 2010 Elsevier Ltd. All rights reserved. Source

Zetterling C.-M.,KTH Royal Institute of Technology
MRS Bulletin | Year: 2015

High-temperature electronic applications are presently limited to a maximum operational temperature of 225°C for commercial integrated circuits (ICs) using silicon. One promise of silicon carbide (SiC) is high-temperature operation, although most commercial efforts have targeted high-voltage discrete devices. Depending on the technology choice, several processing challenges are involved in making ICs using SiC. Bipolar, metal oxide semiconductor field-effect transistors, and junction field-effect transistor technologies have been demonstrated in operating temperatures of up to 600°C. Current technology performance and processing challenges relating to making ICs in SiC are reviewed in this article. © 2015 Materials Research Society. Source

Lehnert B.,KTH Royal Institute of Technology
Physica Scripta | Year: 2013

A review is given on plasma physics and controlled thermonuclear fusion research since the late 1950s and up to the present day. Special emphasis is given to various proposed magnetic plasma confinement systems, as well as to the research aiming at the planned International Thermonuclear Experimental Reactor (ITER) project. The latter is based on the tokamak field geometry of a strong toroidal magnetic field, combined with an inductively imposed toroidal plasma current. Experimental and theoretical research has been conducted on the fundamental problems of confinement, equilibrium, stability, plasma transport and plasma heating. During this development two milestones have been passed on the way to ITER, namely the removed threat by Bohm diffusion at the end of the 1960s, and the discovery of the High Mode at the beginning of the 1980s. Finally, some future perspectives are shortly given on this line of research. © 2013 The Royal Swedish Academy of Sciences. Source

Holzapfel G.A.,University of Graz | Holzapfel G.A.,KTH Royal Institute of Technology | Ogden R.W.,University of Glasgow
Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2010

This review article is concerned with the mathematical modelling of the mechanical properties of the soft biological tissues that constitute the walls of arteries. Many important aspects of the mechanical behaviour of arterial tissue can be treated on the basis of elasticity theory, and the focus of the article is therefore on the constitutive modelling of the anisotropic and highly nonlinear elastic properties of the artery wall. The discussion focuses primarily on developments over the last decade based on the theory of deformation invariants, in particular invariants that in part capture structural aspects of the tissue, specifically the orientation of collagen fibres, the dispersion in the orientation, and the associated anisotropy of the material properties. The main features of the relevant theory are summarized briefly and particular forms of the elastic strain-energy function are discussed and then applied to an artery considered as a thickwalled circular cylindrical tube in order to illustrate its extension-inflation behaviour. The wide range of applications of the constitutive modelling framework to artery walls in both health and disease and to the other fibrous soft tissues is discussed in detail. Since the main modelling effort in the literature has been on the passive response of arteries, this is also the concern of the major part of this article. A section is nevertheless devoted to reviewing the limited literature within the continuum mechanics framework on the active response of artery walls, i.e. the mechanical behaviour associated with the activation of smooth muscle, a very important but also very challenging topic that requires substantial further development. A final section provides a brief summary of the current state of arterial wall mechanical modelling and points to key areas that need further modelling effort in order to improve understanding of the biomechanics and mechanobiology of arteries and other soft tissues, from the molecular, to the cellular, tissue and organ levels. © 2010 The Royal Society. Source

Barsoum Z.,KTH Royal Institute of Technology | Jonsson B.,Volvo
Engineering Failure Analysis | Year: 2011

In this paper a research study has been carried out on the link between weld quality of production welds and the fatigue strength. It has been carried out as a part of a Swedish Technology Platform for lightweight optimised welded structures (LOST), where some of the work packages within the project intend to connect the design and analysis to production and weld quality. One of the results is a new weld quality system from Volvo Group, which has a scientific background, is open for public use and focus on features important for fatigue in welded joints. In this study the emphasis is on a couple of features within the new weld quality system: weld toe radius and the possible existence of weld defects such as cold laps. Large scatter of the local weld geometry was observed for different welding processes. Also the results show that the weld position has a significant effect on the quality and the fatigue resistance of fillet welds and that it may be the difference between normal quality and high quality welds. © 2010 Elsevier Ltd. Source

Lundholm D.,KTH Royal Institute of Technology | Solovej J.P.,Copenhagen University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

A local exclusion principle is observed for identical particles obeying intermediate and fractional exchange statistics in one and two dimensions, leading to bounds for the kinetic energy in terms of the density. This has implications for models of Lieb-Liniger and Calogero-Sutherland type and implies a nontrivial lower bound for the energy of the anyon gas whenever the statistics parameter is an odd numerator fraction. We discuss whether this is actually a necessary requirement. © 2013 American Physical Society. Source

Cvetkovic V.,KTH Royal Institute of Technology
Geophysical Research Letters | Year: 2010

Tracer retention is a key process for the barrier function of crystalline rock to any contaminant. Here we investigate the nature of retention mechanisms and their field-scale parametrization using results of a comprehensive tracer transport experiment in crystalline rock on the field scale (sp Hard Rock Laboratory, Sweden). A method for identifying dominant retention mechanisms and inferring key parameters on the site scale is presented. Taking advantage of multiple tracer tests with a wide range of sorption affinities, retention is shown to be diffusion-controlled. For the considered site, robust features of tracer migration can be reasonably well predicted within a rock volume on at least 200 m scale, by combining independent information with a simple model. © 2010 by the American Geophysical Union. Source

Kroon M.,KTH Royal Institute of Technology
Mechanics of Time-Dependent Materials | Year: 2011

Rubbers and soft biological tissues may undergo large deformations and are also viscoelastic. The formulation of constitutive models for these materials poses special challenges. In several applications, especially in biomechanics, these materials are also relatively thin, implying that in-plane stresses dominate and that plane stress may therefore be assumed. In the present paper, a constitutive model for viscoelastic materials in the finite strain regime and under the assumption of plane stress is proposed. It is assumed that the relaxation behaviour in the direction of plane stress can be treated separately, which makes it possible to formulate evolution laws for the plastic strains on explicit form at the same time as incompressibility is fulfilled. Experimental results from biomechanics (dynamic inflation of dog aorta) and rubber mechanics (biaxial stretching of rubber sheets) were used to assess the proposed model. The assessment clearly indicates that the model is fully able to predict the experimental outcome for these types of material. © Springer Science+Business Media, B. V. 2011. Source

Ansell A.,KTH Royal Institute of Technology
Tunnelling and Underground Space Technology | Year: 2010

The presented investigation combines in situ observations, measurements, testing and theoretical modelling. The in situ work was done to map and evaluate the shrinkage related cracking of shotcrete on short and long sections of soft, plastic drains. The occurrence of variation in shotcrete thickness and crack widths were of particular interest. The theoretical analysis focuses on the stresses that can occur due to uneven drying shrinkage in the two-layered shotcrete. The models used include variation in shotcrete thickness and in time of waiting between turns of spraying, with or without watering of the shotcrete. Watering will delay the shrinkage but has no effect on the strength development. Long times of waiting without watering before spraying a second layer will increase the tensile stresses in the shotcrete. It is recommended that the further work is directed towards establishing guidelines for the design of future drain constructions with shotcrete. Different methods for repair and strengthening of cracked shotcreted drains must be developed, tested and evaluated. © 2010 Elsevier Ltd. Source

Optimal estimation of geopotential coefficients is an important aspect of gravitational field recovery using satellite gravity gradiometry. The combination of gradiometric data and the use of tensor spherical harmonics is useful in this field. Here, we present a new strategy for combining different spectral solutions of the gradiometric boundary value problem by defining and formulating degree-order variance components and using the condition adjustment model. Numerical results show that the spectral combination of considering one degree-order variance component for each type of observation yields better results than the case where one degree-order variance component is estimated for each integral solution of the gradiometric boundary value problem. In this study, the estimates of the variance components are not considered in the standard way; rather, these components are mainly used to absorb the discretization error of the integral solutions. This method is capable of combining integrals in geosciences disciplines. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS). Source

Horlin N.-E.,KTH Royal Institute of Technology
International Journal for Numerical Methods in Engineering | Year: 2010

A novel symmetric weak formulation of Biot's equations for linear acoustic wave propagation in layered poroelastic media is presented. The primary variables used are the frame displacement, the acoustic pore pressure, the scalar potential and the vector potential obtained from a Helmholtz decomposition of the fluid displacement. Also a symmetric weak form based on the frame displacement, the pore pressure and the fluid displacement is obtained as an intermediate result. hp finite element simulations of a double leaf partition based on this new weak formulation is verified against simulation results from the classical frame displacement, fluid displacement formulation and a frame displacement pore pressure formulation. All three formulations simulated, displays the same rate of convergence with respect to finite element bases polynomial degree. The novel formulation also extends a previously published frame displacement, pore pressure, scalar fluid displacement potential formulation with an implicit irrotational fluid displacement assumption to a full representation of Biot's equations. Copyright © 2010 John Wiley & Sons, Ltd. Source

Wikstrom P.-O.H.,University of Cambridge | Ceccato V.,KTH Royal Institute of Technology | Hardie B.,University of Cambridge | Treiber K.,University of Cambridge
Journal of Quantitative Criminology | Year: 2010

Our current understanding of the role of the social environment in crime causation is at best rudimentary. Guided by the theoretical framework of Situational Action Theory, and using data from the ESRC financed Peterborough Adolescent and Young Adult Development Study (PADS+), this paper aims to propose how we can better theorise and study the role of the social environment, particularly the person and place interaction, in crime causation. We will introduce, and illustrate the usefulness of, a space-time budget methodology as a means of capturing people's exposure to settings and describing their activity fields. We will suggest and demonstrate that, combined with a small area community survey and psychometric measures of individual characteristics, a space-time budget is a powerful tool for advancing our knowledge about the role of the social environment, and its interaction with people's crime propensity, in crime causation. Our unique data allows us to study the convergence in time and space of crime propensity, criminogenic exposure and crime events. As far as we are aware, such an analysis has never before been carried out. The findings show that there are (a) clear associations between young people's activity fields and their exposure to criminogenic settings, (b) clear associations between their exposure to criminogenic settings and their crime involvement, and, crucially, (c) that the influence of criminogenic exposure depends on a person's crime propensity. Having a crime-averse morality and strong ability to exercise self-control appears to make young people practically situationally immune to the influences of criminogenic settings, while having a crime-prone morality and poor ability to exercise self-control appears to make young people situationally vulnerable to the influences of criminogenic settings. © Springer Science+Business Media, LLC 2009. Source

Ringstrom H.,KTH Royal Institute of Technology
Communications in Mathematical Physics | Year: 2015

In the subject of cosmology, spatially homogeneous solutions are often used to model the universe. It is therefore of interest to ask what happens when perturbing into the spatially inhomogeneous regime. To this end, we, in the present paper, study the future asymptotics of solutions to Einstein’s vacuum equations in the case of T2-symmetry. It turns out that in this setting, whether the solution is spatially homogeneous or not can be characterized in terms of the asymptotics of one variable appearing in the equations; there is a monotonic function such that if its limit is finite, then the solution is spatially homogeneous and if the limit is infinite, then the solution is spatially inhomogeneous. In particular, regardless of how small the initial perturbation away from spatial homogeneity is, the resulting asymptotics are very different. Using spatially homogeneous solutions as models is therefore, in this class, hard to justify. © 2015, Springer-Verlag Berlin Heidelberg. Source

Larsson E.,KTH Royal Institute of Technology
Annales Henri Poincare | Year: 2015

We prove that compact Cauchy horizons in a smooth spacetime satisfying the null energy condition are smooth. As an application, we consider the problem of determining when a cobordism admits Lorentzian metrics with certain properties. In particular, we prove a result originally due to Tipler without the smoothness hypothesis necessary in the original proof. © 2014, Springer Basel. Source

Marmiroli D.,KTH Royal Institute of Technology
Journal of High Energy Physics | Year: 2016

Abstract: We analyse the phase structure of an N = 2 massive deformation of N = 4 SYM theory on a four-dimensional ellipsoid using recent results on supersymmetric localisation. Besides the ’t Hooft coupling λ, the relevant parameters appearing in the theory and discriminating between the different phases are the hypermultiplet mass M and the deformation (or squashing) parameter Q. Geometric deformation manifests itself as an effective mass term, thus braking the conformal invariance of the theory with massless hypermultiplets. The structure of perturbative corrections around the spherical geometry is analysed in the details and a systematic computational procedure is given, together with the first few corrections. The master field approximation of the matrix model associated to the analytically continued theory in the regime Q ~ 2M and on the compact space is exactly solvable and does not display any phase transition, similarly to N = 2 SU (N) SYM with 2N massive hypermultiplets. In the strong coupling limit, equivalent in our settings to the decompactification of the four-dimensional ellipsoid, we find evidence that the theory undergoes an infinite number of phase transitions starting at finite coupling and accumulating at λ = 8. Quite interestingly, the threshold points at which transitions occur can be pushed towards the weak coupling region by drifting Q to the value 2M. © 2016, The Author(s). Source

Flener E.B.,KTH Royal Institute of Technology
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2010

The paper presents the performance of four long-span deep-corrugated steel box culverts with spans of 8- and 14-m during backfilling, as well as comparisons with finite-element modeling and design codes. Two of the culverts were stiffened at the crown arch. The test results show that the stiffening applied on the culverts is quite effective. The crown rises of the respective stiffened culverts were found to be half those of the not-stiffened culverts. The influence of the structure geometry on the soil-passive earth pressure was confirmed, as well as the sensitivity of box culverts to soil loads with increasing spans. The results showed that the influence of the size and shape of the box culverts on the amount of thrusts must be better implemented in the design method. The finite-element analysis results were conservative when live loading was concerned but the crown displacements and thrust during backfilling were underestimated. © 2010 ASCE. Source

Guruswami V.,Carnegie Mellon University | Hastad J.,KTH Royal Institute of Technology | Kopparty S.,Institute for Advanced Study
IEEE Transactions on Information Theory | Year: 2011

The list-decodability of random linear codes is shown to be as good as that of general random codes. Specifically, for every fixed finite field F q,p, ∈ (0,1 -1/q) and ε > 0 it is proved that with high probability a random linear code C in Fq n of rate (1-Hq(p)-ε can be list decoded from a fraction p of errors with lists of size at most O(1/ε). This also answers a basic open question concerning the existence of highly list-decodable linear codes, showing that a list-size of O (1/ε) suffices to have rate within ε of the information-theoretically optimal rate of 1-Hq(p). The best previously known list-size bound was qO(1/ε) (except in the q =2 case where a list-size bound of O(1/ε) was known). The main technical ingredient in the proof is a strong upper bound on the probability that random vectors chosen from a Hamming ball centered at the origin have too many (more than Ω (ℓ)) vectors from their linear span also belong to the ball. © 2006 IEEE. Source

Heisenberg L.,KTH Royal Institute of Technology | Heisenberg L.,The Oskar Klein Center
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

In this work we study different classes of effective composite metrics proposed in the context of one-loop quantum corrections in bimetric gravity. For this purpose we consider contributions of the matter loops in the form of cosmological constants and potential terms yielding two types of effective composite metrics. This guarantees a nice behavior at the quantum level. However, the theoretical consistency at the classical level needs to be ensured additionally. It turns out that among all these possible couplings, only one unique effective metric survives these criteria at the classical level. © 2015 American Physical Society. Source

Hossenfelder S.,KTH Royal Institute of Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

We show that analog gravity systems exist for charged, planar black holes in asymptotic anti-de Sitter space. These black holes have been employed to describe, via the gauge-gravity duality, strongly coupled condensed matter systems on the boundary of anti-de Sitter (AdS) space. The analog gravity system is a different condensed matter system that, in a suitable limit, describes the same bulk physics as the theory on the AdS boundary. This combination of the gauge-gravity duality and analog gravity therefore suggests a duality between different condensed matter systems. © 2015 American Physical Society. Source

Norstrom P.,KTH Royal Institute of Technology
International Journal of Technology and Design Education | Year: 2013

Engineers commonly use rules, theories and models that lack scientific justification. Examples include rules of thumb based on experience, but also models based on obsolete science or folk theories. Centrifugal forces, heat and cold as substances, and sucking vacuum all belong to the latter group. These models contradict scientific knowledge, but are useful for prediction in limited contexts and they are used for this when convenient. Engineers' work is a common prototype for the pupils' work with product development and systematic problem solving during technology lessons. Therefore pupils should be allowed to use the engineers' non-scientific models as well as scientific ones when doing design work in school technology. The acceptance of the non-scientific models for action guidance could be experienced as contradictory by pupils and teachers alike: a model that is allowed, or even encouraged in technology class is considered wrong when doing science. To account for this, different epistemological frameworks must be used in science and technology. Technology is first and foremost what leads to useful results, not about finding the truth or generally applicable laws. This could cause pedagogical problems, but also provide useful examples to explain the limitations of models, the relation between model and reality, and the differences between science and technology. © 2011 Springer Science+Business Media B.V. Source

Lin J.,KTH Royal Institute of Technology
Journal of Transport Geography | Year: 2012

Aviation systems are less geographically constrained compared to ground transportation because their routes are not so affected by geographical conditions. For this reason, aviation systems are endowed to some extent with a distinctive network topology and spatial pattern. In this article, the statistical features of China's aviation system (CAS) are investigated through a complex network approach by examining weekly flight patterns. The correlation study proves the existence of a spatial hierarchical structure within China's aviation network, which implies a more complex spatial mechanism. Subsequently the spatial structure of CAS is explored based on the flight distances between airport cities. In light of three measurements of node strength, population and GDP, It has been decided that the spatial effect of China's aviation system should be analyzed separately in term of different distance scales. Only for medium- and long-distance travel, the flight patterns conform to a gravitation law; therefore, the distance dependence function can be generalized as a scaling relationship. In summary, from a complex network angle, this paper provides preliminary but enlightening insights to understanding the unique spatial mechanism of aviation systems. © 2011 Elsevier Ltd. Source

Life cycle assessment (LCA) is explored as an analytical tool in strategic environmental assessment (SEA), illustrated by case where a previously developed SEA process was applied to municipal energy planning in Sweden. The process integrated decision-making tools for scenario planning, public participation and environmental assessment. This article describes the use of LCA for environmental assessment in this context, with focus on methodology and practical experiences. While LCA provides a systematic framework for the environmental assessment and a wider systems perspective than what is required in SEA, LCA cannot address all aspects of environmental impact required, and therefore needs to be complemented by other tools. The integration of LCA with tools for public participation and scenario planning posed certain methodological challenges, but provided an innovative approach to designing the scope of the environmental assessment and defining and assessing alternatives. © 2011 Elsevier Inc. Source

Nosko O.,KTH Royal Institute of Technology
Tribology Letters | Year: 2016

The instability of sliding causes deterioration of performance characteristics of tribosystems and is undesired. To predict its occurrence, the motion of a body of a one-degree-of-freedom system with friction is investigated about the steady sliding equilibrium position. The motion equation is formulated with the friction coefficient dependent on the sliding velocity and contact temperature changing due to transient heat conduction in the body. An analytical expression for the body motion is derived using the Laplace integral transform. It is shown that the sliding instability can manifest in the form of deviation of the body from the equilibrium position or in the form of oscillation. The instability conditions containing the friction-velocity and friction-temperature slope coefficients are obtained. Positive friction-temperature slope results in the deviation of the body from the equilibrium position. At negative friction-temperature slope, both types of the sliding instability can occur. The proposed instability conditions agree well with existing theoretical concepts and can be useful when designing tribosystems. © Springer Science+Business Media New York 2015. Source

Powell S.,University of Maryland University College | Powell S.,KTH Royal Institute of Technology
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

Conventional ordering transitions, described by the Landau paradigm, are characterized by the symmetries broken at the critical point. Within the constrained manifold occurring at low temperatures in certain frustrated systems, unconventional transitions are possible that defy this type of description. While the critical point exists only in the limit where defects in the constraint are vanishingly rare, unconventional criticality can be observed throughout a broad region of the phase diagram. This work presents a formalism for incorporating the effects of such defects within the framework of scaling theory and the renormalization group, leading to universal results for the critical behavior. The theory is applied to two transitions occurring within a model of spin ice, and the results are confirmed using Monte Carlo simulations. Relevance to experiments, particularly in the spin-ice compounds, is discussed, along with implications for simulations of related transitions, such as the cubic dimer model and the O(3) sigma model with "hedgehog" suppression. © 2013 American Physical Society. Source

Hulten M.,KTH Royal Institute of Technology
International Journal of Technology and Design Education | Year: 2013

In the state-of-the-art Glass Project run by the Swedish National Agency for Education during the second half of the 1960s, a new type of comprehensive technology education was developed. The project had little impact on school practice and was soon forgotten about. However, the project is interesting from several points of view. First, it elaborated an interesting curricular idea where school activities were to centre around technology, thus creating a meaningful whole for the pupils, a sort of "language of schooling". Second, the Glass Project illustrates a utopian logic of educational reform. The school had become an important area of reform in the mid-twentieth century, and in this the pedagogy of the "old school" was heavily criticised. Technology education clearly became a tool for progressive ideas in Sweden in the 1960s. © 2012 Springer Science+Business Media B.V. Source

Metzger J.,KTH Royal Institute of Technology | Schmitt P.,Nordic Center for Spatial Development
Environment and Planning A | Year: 2012

This paper investigates the first ever so-called 'macroregional strategy' developed under the aegis of the European Commission: the European Union Strategy for the Baltic Sea Region (EUSBSR). Through a drawing together of elements of actor-network theory and regionalization theory, it is argued that the adoption of the EUSBSR can be seen as a milestone within a wider process towards Baltic Sea regionalization, whereby the Baltic Sea region is increasingly 'solidified' through the positioning of the European Commission as a spokesperson for the interests of the region. It is further suggested that, if not seriously contested, the possible acceptance of the European Commission as a designated regional spokesperson might be a crucial step in a process whereby the soft space of the Baltic Sea Region may gradually become more formalized. Nonetheless, caution must be taken so as not to confuse degrees of formal institutional fixity with degrees of durability. © 2012 Pion Ltd and its Licensors. Source

Soder L.,KTH Royal Institute of Technology
IEEE Transactions on Power Systems | Year: 2010

The requirements concerning reliability in power supply are high. This paper treats the issue of system adequacy, i.e., there should be enough installed capacity to meet the load with an acceptable reliability. The challenge in a liberalized market is that the utilization time of rarely used peak units is so low that they require extremely high prices in order to be profitable. This has led to different methods, including the creation of capacity markets. The aim of this paper is to analyze the connection between peak prices, system reliability, required amount of subsidized capacity, i.e., the volume of the capacity market. In the studied market setup, only some selected units, so-called reserve plants, receive a capacity payment. The paper also provides an example concerning change of capacity market volume in presence of wind power. © 2010 IEEE. Source

Dirks B.,KTH Royal Institute of Technology | Enblom R.,Bombardier
Wear | Year: 2011